,transcriber's ,note3 ,bold text is surrounded by equal signs and italic text is surrounded by underscores4 ,,war ,,department ,,office ,,of ,,the ,,chief ,,signal ,,officer ,,manual ,no4 #f ,,visual ,,signaling ,,signal ,,corps ,,united ,,states ,,army #aiaj ,illustration ,,washington ,,government ,,printing ,,office #aiaj ,,war ,,department1 ,document ,no4 #cff4 ,,office ,,of ,,the ,,chief ,,signal ,,officer4 ,,war ,,department1 ,,office ,,of ,,the ,,chief ,,of ,,staff1 ,washington1 ,april #bj1 #aiaj4 ,the following ,manual of ,visual ,signaling1 prepared in the ,office of the ,chief ,signal ,officer1 is approved and herewith published for the information and guidance of the ,regular ,army and the ,organized ,militia of the ,united ,states1 and supersedes all other pamphlets or similar instructions heretofore issued upon the subject4 ,officers and men of the ,signal ,corps will thoroughly familiarize themselves with the instructions and suggestions contained herein4 ,by order of the ,secretary of ,war4 ,,tasker ,h4 ,,bliss1 ,brig4 ,general1 ,general ,staff1 ,acting ,chief of ,staff4 ,,table ,,of ,,contents4 ,page4 ,,chapter ,i4--,,introduction #i ,,chapter ,,ii4--,visual signaling equipment4 ,the wand #aa ,the flag kit3 ,the #b-;foot flag kit #ab ,the #d-;foot flag kit #ab ,care of flag material #ac ,powers and limitations of flag signaling #ac ,the heliograph3 ,historical #ad ,description #ad ,assembling #ag ,adjustment #bj ,operation #ba ,care of apparatus #bb ,powers and limitations of the heliograph #bb ,the signal lantern3 ,acetylene #bc ,calcium carbide #bc ,method of gas generation #bd ,description #be ,operation and care #cj ,powers and limitations of the signal lantern #ce ,rockets and shells3 ,description #ce ,operation #ch ,employment #dj ,the semaphore3 ,description #dj ,the searchlight3 ,methods of employment #da ,the ,coston signals #da ,very's night signals #db ,the ,ardois system of signaling #db ,sound signals #dd ,improvised signal methods #dd ,,chapter ,,iii4--,alphabets or systems of signals4 ,signal alphabets3 ,american ,morse #de ,continental ,morse #de ,army and navy #de ,abbreviations #df ,code calls #dg ,execution of signal alphabets #dg ,the army and navy alphabet #dg ,the ,morse alphabets #di ,international code of signals3 ,description #ea ,two-arm semaphore #ea ,the ,ardois system #eb ,coston signals #ed ,very's night signals #ed ,rocket signaling #ee ,two-arm semaphore alphabet1 ,u4 ,s4 ,navy #eg ,summary of signals1 army and navy alphabet #fj ,,chapter ,,iv4--,the field message4 ,definition #fd ,the blank form #fd ,writing the message #ff ,instructions to operators3 ,use of message blank #ff ,duties of sending operators #ff ,order of transmission #ff ,duties of receiving operators #fg ,communications confidential #fg ,checking the message #fg ,,chapter ,v4--,the signal station4 ,location of stations3 ,general considerations #fh ,backgrounds #gj ,azimuth of stations #ga ,altitude #ga ,determination of background color #gb ,choice of apparatus #gc ,miscellaneous considerations #gc ,intervisibility table #gd ,finding a station #ge ,operation of stations3 ,personnel #gf ,calls and personal signals #gh ,opening communication #gi ,commencing the message #hj ,sending and receiving #hj ,breaking #hj ,discontinuance of transmission #ha ,acknowledgment of receipt #ha ,station records #ha ,formation of signals #hb ,repeating the message #hc ,signal practice #hc ,,chapter ,,vi4--,codes and ciphers4 ,codes in use #hd ,employment of codes #hd ,cipher code #he ,the ,war ,department ,code #hf ,cipher code in field work #hg ,field ciphers3 ,description and use #hg ,forms of field cipher #hh ,inversions #hh ,concealment of terminations #hh ,cipher apparatus3 ,the cipher disk #hi ,the mathematical cipher #ic ,the route cipher #id ,cipher detection3 ,employment of cipher disk #if ,,chapter ,,vii4--,field glasses and telescopes4 ,reflection #ih ,refraction #ih ,lenses #ih ,focus #ii ,optical center #ii ,image #ii ,conjugate foci #ii ,law of foci #ajj ,formation of image #aja ,spherical aberration #ajb ,chromatic aberration #ajb ,telescopes #ajd ,galilean field glasses and telescopes #ajf ,porro prism field glasses and telescopes #ajf ,field glasses #ajh ,properties of telescopes and field glasses #aji ,power #aji ,light #aaa ,field #aad ,definition #aae ,field glasses and telescopes issued by the ,signal ,corps #aai ,type ,a #aba ,type ,b #abd ,type ,c #abe ,type ,d #abe ,field-glass specifications #abf ,,chapter ,i4 ,,introduction4 ,while1 in consequence of the development of electrical invention and improvement1 visual signaling will be less frequently resorted to in future than heretofore in the service of field lines of information1 it should be appreciated that the necessity for an adequate supply of apparatus of this kind1 and the need for skilled manipulators to operate it1 has in no wise diminished4 ,the great celerity with which electric signals can be exchanged and their usual entire independence of local conditions has placed systems of this class foremost among the signaling methods of the world4 ,there is scarcely any commercial industry whose successful existence does not vitally depend upon some one1 perhaps several systems of signaling1 and improvements of old and inventions of new signal devices are continually necessary to meet the requisite needs demanded by the progress of art and science4 ,railways are probably the greatest of all commercial users of signals4 ,with them the great mass of intelligence is transmitted by the electric telegraph and telephone1 but the flag1 the semaphore1 the signal light1 and many other contrivances furnish indispensable visual adjuncts4 ,visual signaling is and always will be a most valuable means of transmitting information in peace and war1 and it is not to be imagined that it will ever be supplanted in its particular function by the introduction of other methods4 ,occasions will frequently occur in the field when no other means will be practicable1 and then1 if not before1 will the value of the system be fully emphasized4 ,strictly speaking1 a visual signal is any visible sign by which intelligence is communicated1 but in a military sense the term visual signaling has a broader meaning and includes other methods of transmitting information than those which appeal to the sense of sight4 ,in most systems of signals suitable for military use1 each signal is composed of one or more separate units1 known as elements4 ,having prescribed a certain number of elements1 the various signals are formed by having these elements appear singly or together in different arrangements or combinations4 ,the continental system is one of two elements1 namely the dot and the dash1 while the ,morse system employs three elements1 the dot1 the dash1 and the space4 ,having agreed upon a certain number of combinations of elements1 a system of signals is formed by giving a meaning to each combination4 ,these meanings usually include the letters of the alphabet and numerals1 combinations of which being used to formulate necessary information4 ,combinations of elements of any system can also1 however1 be used to indicate any desired meaning4 ,with reference to period of visibility1 signals are of two kinds1 transient and permanent4 ,a transient signal is one which disappears as soon as completed2 a permanent signal is one that remains in view for some time4 ,heliograph signals are transient signals1 while signals made by code flags are permanent signals4 ,signals are divided into classes in accordance with the number of elements employed in their formation4 ,thus1 signals using two elements are signals of the second class1 signals using three elements signals of the third class1 etc4 ,the standard apparatus used in visual signaling is fully described in a succeeding chapter4 ,some of the instruments employed are used wholly for day1 and some wholly for night1 signaling4 ,some devices1 either with or without slight variations1 are equally well adapted to day or night work4 ,visual signaling presents a great field for ingenious and resourceful work1 and emergency will often demand the advantageous employment of other methods than those described herein4 ,,chapter ,,ii4 ,,visual ,,signaling ,,equipment4 ,,the ,,wand4 ,the wand is a stick of light wood about #ah inches long and one-half inch in diameter4 ,it is held loosely between the thumb and forefinger and waved rapidly to the right or left to indicate the elements of the alphabet4 ,it is used for practice purposes and the signals made by it are only intended to be read at very short distances4 ,,the ,,flag ,,kit4 ,two kinds of flag kits1 the #b-;foot kit and the #d-;foot kit1 are issued by the ,signal ,corps4 ,the #b-;foot kit4--,this kit consists of one white and one red signal flag1 two three-jointed staffs1 and a suitable carrying case to contain the outfit4 ,the white flag is made of white muslin #b feet square1 with an #h-;inch turkey-red muslin center4 ,the red flag is of similar size and material1 the only difference being an alternation of colors in the body and center4 ,the means of attachment to the staff consists of a loop at the center1 and two ends of white tape at each edge1 of the back of the flag body4 ,the staff is made of hickory in three joints1 each #bc inches long1 and is assembled by telescoping into brass ferrules4 ,brass eyes are provided on the first and second joints to receive the tape ends at the edge of the flag4 ,the carrying case1 of convenient size and shape to contain the two flags and staffs complete1 is made of #h-ounce standard khaki bound with leather and fitted with a shoulder strap4 ,the #b-;foot kit is essentially a practice kit1 although under favorable conditions of weather and terrain it may be used to advantage as a short distance service signaling outfit4 ,two of these kits are issued to each troop1 battery1 and company for the purpose of disseminating general instruction in military signaling throughout the army4 ,the #d-;foot kit4--,this kit is of essentially the same description as the #b-;foot kit except as regards size4 ,the flags are #c feet #i inches square with #ab-;inch centers and the staffs are considerably heavier1 the joints being each #cf inches long4 ,the #d-;foot kit is the standard field flag kit and the range at which signals can be exchanged with it depends on a variety of factors1 such as the condition of the weather1 the location of stations1 the proficiency of signalmen1 etc4 ,the speed for continuous signaling is seldom greater than five to six words per minute4 ,care of flag material4--,signal flags should be examined at the close of drill or practice and repairs made to any rents or loose ties discovered4 ,flags1 when soiled1 should be thoroughly washed and dried in the sun4 ,signals made by clean flags are much more easily read than those made by dirty ones4 ,staffs should be handled with care1 especially when jointing or unjointing4 ,care should be taken not to bruise the ends of the brass ferrules4 ,if a ferrule becomes loose on a staff it should be tightened without delay4 ,powers and limitations of flag signaling4--,the advantages which may be claimed for this method of signaling are portability of apparatus1 adaptability to varied weather conditions1 and great rapidity of station establishment4 ,the disadvantages are the lack of celerity of the signals1 their impenetrability to dust or smoke1 and the comparatively short ranges at which they can be read4 ,,the ,,heliograph4 ,the heliograph is an instrument designed for the purpose of transmitting signals by means of the sun's rays4 ,historical4--,experiments with the heliograph with a view to its adoption as a part of the visual signaling equipment of the ,united ,states ,army were commenced as early as #ahgh4 ,the reported successful use of the instrument by the ,british in ,india about this time led to the importation of two heliographs of the ,mance pattern4 ,a series of experiments with these machines conducted for the purpose of eliminating certain objectionable features finally resulted in the evolution of the present type of service heliograph4 ,the early ,english heliograph was not provided with a shutter1 the flash being directed on the distant station by means of a movable mirror controlled by a key4 ,the great objection to this type of instrument was the impossibility of maintaining accurate adjustment during the transmission of signals due to the fact that the manipulation of the mirror tended to throw the flash constantly out of alignment4 ,to overcome this1 the ,american heliograph has been provided with a screen designed to operate as a shutter and control the flash reflected from an immobile mirror4 ,description4--,the service heliograph equipment of the ,signal ,corps consists of3 ,a sole-leather pouch with shoulder strap containing-- #a sun mirror4 #a station mirror4 ,inclosed in a wooden box4 #a screen1 #a sighting rod1 #a screw-driver4 ,a small pouch1 sliding by #b loops upon the strap of the larger pouch1 containing #a mirror bar4 ,a skeleton leather case containing #b tripods4 ,illustration3 ,,fig4 #a4--;,heliograph assembled4 ,the mirrors are each #d-;inch squares of plate glass supported by sheet brass and cardboard backings1 and mounted in brass retaining frames4 ,at the center of each mirror there is an unsilvered spot three thirty-seconds of an inch in diameter and holes corresponding to these spots are drilled in the backing4 ,the sun mirror differs from the station mirror only in that it has a paper disk pasted upon its face covering the unsilvered spot4 ,the mirror frames are carried by brass supports provided at the bases with conical projections accurately turned to fit the sockets of the mirror bar and grooved at the ends to receive the clamping spring4 ,each support is fitted with a tangent screw and worm wheel attachment functioned to control the motion of the mirror frame about its horizontal axis4 ,illustration3 ,,fig4 #b4--,mirror and mirror bar case4 ,the mirror bar is a bronze casting provided at the center with a clamp threaded to fit the screw of the tripod4 ,by releasing the clamp the bar may be moved independently of the screw and adjusted to any desired position4 ,conical sockets for the reception of the mirror supports are provided at the ends of the mirror bar4 ,these sockets work freely in the bar and1 being actuated by a tangent screw and worm wheel1 serve to regulate the motion of the mirror frame about its vertical axis4 ,clamp springs1 for engaging and securing the ends of the mirror frame supports1 are attached at each end of the bar4 ,the screen is a brass frame #f inches square1 in which six segments or leaves are mounted in such a way as to form a shutter4 ,the leaves are designed to turn through arcs of #ij on horizontal axes1 unanimity of movement being secured by connections made with a common crank bar4 ,the crank bar is operated by a key and retractile spring which serve to reveal and cut off the flash4 ,a set screw and check nut at the lower edge of the screen frame limits the motion of the crank bar and the opening of the leaves4 ,a threaded base support furnishes the means of attaching the screen frame to the tripod4 ,the sighting rod is a brass rod #f inches long1 carrying at the upper end a front sight and a movable disk4 ,about the rod is fitted a movable bronze collar1 coned and grooved to take the socket and clamping spring of the mirror bar4 ,a milled edged bronze washer serves to clamp the collar to the rod at any desired point4 ,illustration3 ,,fig4 #c4--;,heliograph tripods4 ,the tripods are similar in all respects1 the screw of either threading into the mirror bar or screen frame4 ,each tripod is provided with a hook at the base of the head1 allowing the suspension of a weight when great stability is required4 ,assembling4--,there are two ways of assembling the heliograph and the position of the sun is the guide in determining which of the two should1 in any given case1 be employed4 ,when the sun is in front of the operator 7that is1 in front of a plane through his position at right angles to the line joining the stations7 the sun mirror only is required2 with the sun in rear of this plane both mirrors should be used4 ,with one mirror the rays of the sun are reflected directly from the sun mirror to the distant station2 with two mirrors1 the rays are reflected from the sun mirror to the station mirror1 and thence to the distant station4 ,with one mirror3 ,firmly set one of the tripods upon the ground2 attach the mirror bar to the tripod2 insert and clamp in the sockets the sun mirror and sighting rod1 the latter having the disk turned down4 ,at a distance of about #f inches1 sight through the center of the unsilvered spot in the mirror and turn the mirror bar1 raising or lowering the sighting rod until the center of the mirror1 the extreme point of the sighting rod1 and the distant station are accurately in line4 ,firmly clamp the mirror bar to the tripod1 taking care not to disturb the alignment1 and turn up the disk of the sighting rod4 ,the mirror is then moved by means of the tangent screws until the shadow spot falls upon the paper disk in the sighting rod1 after which the flash will be visible at the distant station4 ,the shadow spot is readily found by holding a sheet of paper or the hand about #f inches in front of the mirror1 and should be constantly kept in view until located upon the disk4 ,the screen is attached to a tripod and established close to1 and in front of1 the sighting disk1 in such a way as to intercept the flash4 ,with two mirrors3 ,firmly set one of the tripods on the ground2 clamp the mirror bar diagonally across the line of vision to the distant station2 clamp the sun mirror facing the sun to one end of the mirror bar and the station mirror facing the distant station4 ,stooping down1 the head near and in rear of the station mirror1 turn the sun mirror by means of its tangent screws until the whole of the station mirror is seen reflected in the sun mirror and the unsilvered spot and the reflection of the paper disk accurately cover each other4 ,still looking into the sun mirror1 adjust the station mirror by means of the tangent screws until the reflection of the distant station is brought exactly in line with the top of the reflection of the disk and the top of the unsilvered spot of the sun mirror2 after this the station mirror must not be touched4 ,now step behind the sun mirror and adjust it by means of the tangent screws so that the shadow spot falls upon the center of the paper disk on the station mirror4 ,the flash will then be visible at the distant station4 ,the screen and its tripod are established as described in the single mirror assembling4 ,alternate method with two mirrors3 ,clamp the mirror bar diagonally across the line of vision to the distant station1 with the sun mirror and the station mirror approximately facing the sun and distant station1 respectively4 ,look through small hole in sun mirror and turn the station mirror on its vertical and horizontal axes until the paper disk on the station mirror accurately covers the distant station4 ,standing behind sun mirror1 turn it on its horizontal and vertical axes by means of the tangent screw attachments until the shadow spot falls upon the paper disk on station mirror4 ,adjustment4--,perfect adjustment is maintained only by keeping the shadow spot uninterruptedly in the center of the paper disk1 and as this spot continually changes its position with the apparent movement of the sun1 one signalman should be in constant attendance on the tangent screws of the sun mirror4 ,movement imparted by these screws to the mirror does not disturb the alignment1 as its center 7the unsilvered spot7 is at the intersection of the axes of revolution4 ,extra care bestowed upon preliminary adjustment is repaid by increased brilliancy of flash4 ,with the alignment absolutely assured and the shadow spot at the center of the disk1 the axis of the cone of reflected rays is coincident with the line of sight and the distant station receives the greatest intensity of light4 ,remember the distant observer is unquestionably the better judge as to the character of the flash received2 and if therefore1 adjustment is called for when the shadow spot is at the center of the disk1 the alignment is probably at fault and should be looked after at once4 ,in setting up the tripods always see that the legs have a sufficient spread to give a secure base and on yielding soil press firmly into the ground4 ,keep the head of the tripod as nearly level as possible and in high wind ballast by hanging a substantial weight to the hook4 ,see that the screen completely obscures the flash2 also that the flash passes entire when the screen is opened4 ,this feature of the adjustment is partially regulated by the set screw attached to the screen frame4 ,the retractile spring should sharply return all the leaves of the screen to their normal positions when the key is released4 ,failure to respond promptly is obviated by strengthening or replacing the spring4 ,operation4--,it is of the utmost importance that uniformity in mechanical movement of the screen be cultivated1 as lack of rhythm in the signals of the sender entails breaks and delay on the part of the receiver4 ,dark backgrounds should1 when practicable1 be selected for heliograph stations1 as the signals can be most easily distinguished against them4 ,to find a distant station1 its position being unknown1 reverse the catch holding the station mirror and with the hand turn the mirror very slowly at the horizon over the full azimuth distance in which the distant station may possibly lie4 ,this should be repeated not less than twice1 after which1 within a reasonable time1 there being no response1 the mirror will be directed upon a point nearer the home station and the same process repeated4 ,with care and intelligence it is quite probable that1 a station being within range and watching for signals from a distant station with which it may be desired to exchange messages1 this method will rarely fail to find the sought-for station4 ,the exact direction of either station searching for the other being unknown1 that station which first perceives that it is being called will adjust its flash upon the distant station to enable it when this light is observed to make proper adjustments4 ,if the position of each station is known to the other1 the station first ready for signaling will direct a steady flash upon the distant station to enable the latter to see not only that the first station is ready for work1 but to enable the distant station to adjust its flash upon the first station4 ,smoked or colored glasses are issued for the purpose of relieving the strain on the eyes produced by reading heliograph signals4 ,care of apparatus4--,minor parts of the instrument should be dismounted only to effect repairs1 for which spare parts are furnished on requisition4 ,steel parts should be kept oiled and free from rust4 ,tangent screws and bearings should be frequently inspected for dust or grit4 ,mirrors should invariably be wiped clean before using4 ,in case of accident to the sun mirror1 the station mirror can be made available for substitution therefor by removing the paper disk4 ,if the tripod legs become loose at the head joints1 tighten the assembling screws with the screw-driver4 ,powers and limitations of the heliograph4--,portability1 great range1 comparative rapidity of operation1 and the invisibility of the signals except to observers located approximately on a right line joining the stations between which communication is had1 are some of the advantages derived from using the heliograph in visual signaling4 ,the principal disadvantage results from the entire dependence of the instrument upon the presence of sunlight4 ,the normal working range of the heliograph is about #cj miles1 though instances of its having attained ranges many times greater than this are of record4 ,the heliograph can be depended upon to transmit from five to twelve words per minute4 ,,the ,,acetylene ,,lantern4 ,the signal lantern is an instrument designed for the purpose of transmitting signals by means of intermittent flashes of artificial light4 ,it is the standard night visual signaling equipment furnished by the ,signal ,corps and depends for its illumination upon the combustion of acetylene gas4 ,acetylene4--,acetylene is a pure hydrocarbon gas1 producible in various ways1 the commoner of which are3 7a7 ,by dropping calcium carbide into water2 7b7 by dropping water upon calcium carbide4 ,this gas gives1 when burning1 high penetrative power1 and was first described by ,mr4 ,edmund ,davy1 professor of chemistry to the ,royal ,dublin ,society1 in #ahcf4 ,calcium carbide4--,in the manufacture of calcium carbide for commercial purposes the best quality of coke and quicklime are used4 ,these two substances are powdered thoroughly1 mixed in proper proportions1 and then placed in an electrical furnace4 ,under the action of the intense heat 7#e1ejj ,f47 these two refractory substances unite and form calcium carbide4 ,calcium carbide is of a grayish-white color1 crystal in appearance1 and is nonexplosive and noncombustible1 being1 except for its affinity for water1 an absolutely inert substance4 ,a pound of commercial carbide will produce approximately #e cubic feet of gas4 ,when water is brought in contact with calcium carbide1 the generation of acetylene is rapid2 owing to its strong affinity for water it will become air slacked and slowly lose its strength if exposed to the action of the moisture in the atmosphere2 consequently1 when stored or being transported it should be kept in air-tight cans4 ,when calcium carbide is brought in contact with water1 the following occurs3 ,as is known1 the principal components of water are oxygen and hydrogen1 and calcium carbide is calcium and carbon4 ,when brought in contact1 the oxygen in the water decomposes the calcium in the carbide1 and in this decomposition the hydrogen in the water is liberated and unites with the carbon of the carbide1 forming a hydrocarbon gas which is acetylene4 ,it is a pure white light of intense brilliancy and high candlepower4 ,the spectrum analysis of acetylene shows that it is almost identical with sunlight1 and in consequence delicate shades of color appear according to their true value as under the light of the sun1 consequently it penetrates fog to a greater distance than other lights4 ,acetylene is like other gases--explosive when mixed with air in proper proportions1 confined1 and ignited--and the same precautions should therefore be taken in its use as would be in the handling of coal or water gas1 gasoline vapor1 etc4 ,as acetylene is very rich in carbon1 it will not burn in its pure state without smoking4 ,to avoid this1 burners have been constructed so that the gas is mixed with the proper proportion of air at the burner tip1 to insure perfect combustion4 ,the burners for acetylene are different from those for other gases4 ,in order to get a flat flame1 the gas is brought through two perfectly round holes at an angle which causes the two flames to impinge upon each other and thus form a flat flame4 ,method of gas generation4--,the method employed for producing acetylene in the signal lantern is by bringing water into contact with calcium carbide4 ,the disadvantage of this method is that when the water is not in excess and does not entirely surround and touch each piece of carbide the heat of generation will so change the chemical properties of the gas that combustion at the burners is not satisfactory4 ,this change is technically known as polymerization1 or the breaking up of acetylene into other hydrocarbons1 such as vapors of benzine1 benzole1 etc4 ,these form a tarry substance which is apt to condense at the burner tip and clog the openings4 ,also they deposit carbon on the burners1 as they require more air for perfect combustion than does pure acetylene4 ,another disadvantage of this system is that after the carbide and water are in contact1 generation of gas will continue until all the water is absorbed4 ,where1 however1 portability of the generating apparatus is desired and resort to this method is necessary1 the objections are not important1 if the apparatus is well constructed and care is taken in its use4 ,description4--,this equipment consists of a signal lantern with cartridge generator attached4 ,the lantern is equipped with a special aplanatic lens mirror1 #e inches in diameter and about #c inches focus4 ,the lantern is packed complete in a wooden case with shoulder straps and the following extra parts are included1 each part having its own receptacle in the case3 #b burners2 #a cover glass2 #c cartridges of calcium carbide of #e ounces each2 #a pair of gas pliers2 #a tube white lead2 #a extra filter bag2 #a screw-driver4 ,illustration3 ,,fig4 #d4--,the signal lantern4 ,the lantern is made of brass1 all parts of which are riveted4 ,the burner is of the double tip form1 consuming three-quarters of a cubic foot per hour4 ,the lantern is fitted with a hood to provide proper ventilation and at the same time to prevent the flickering of the light by the wind4 ,the front door of the lantern is hinged and fastens with a spring clasp2 it is so arranged that it can be entirely removed if necessary4 ,the cover glass is made in three sections and is not affected by the expansion and contraction of the metal due to changes in temperature4 ,the glass is fastened by the aid of a spring wire1 so that it can be readily removed if it is necessary to replace a broken section4 ,in the base of the lantern is a key and the adjustment for regulating the height of the flame4 ,the key is so arranged that when not depressed but little gas is admitted through the by-pass to the burner and the flame is low4 ,by depressing the key as much gas as can be entirely consumed is admitted to the burner1 which gives a bright flash4 ,at the back of the lantern there is an adjustable handle1 so that the equipment can be used as a hand lantern if desired4 ,this form of lantern can be used with the regular heliograph tripod1 the generator being either attached to the back of the lantern or suspended1 as shown in figure #d4 ,when practicable it is better to attach the generator to the lantern1 as shown in figure #e4 ,the candlepower of this lantern is about #a1ijj4 ,illustration3 ,,fig4 #e4 ,the generator used is known as the cartridge generator1 and while constructed on the water-feed principle1 the disadvantages incident to this method are eliminated as far as possible4 ,it is constructed of brass and has a removable top4 ,attached to the inside of the top is a flexible frame with a spring latch1 the spring latch being hinged4 7,fig4 #h47 ,at the top of the frame is a tube or cylinder1 the bottom of which is conical in shape and covered by a rubber plug4 ,at the bottom of the frame is a hollow tube1 which is the water inlet4 ,the cartridge proper consists of a tin cylinder1 having an opening at either end4 ,a small cylinder of wire mesh extends from and connects these openings4 ,the carbide lays around this mesh on the inside of the cartridge4 ,the rubber plug before mentioned fits into the upper opening1 and the water tube into the lower opening4 7,see figs4 #g1 #h1 and #i47 ,inside the tube1 at the top of the frame1 is a filter1 the function of which is to remove the dust and moisture from the gas4 ,the outlet from this chamber is by a brass bent tube having a stopcock attached thereto4 ,figure #f gives a sectional view of the generator with the cartridge in place4 ,d ,f ,g ,h represent the valve frame and ,i the cartridge attached4 ,the reservoir ,a is filled with water1 and when the frame is immersed1 with the valve ,r closed1 the air contained in the cartridge and tubing can not escape1 the water seal preventing1 while the confined air prevents the water from rising in the tube ,n4 ,when the valve at ,r is opened and the air is allowed to escape1 part of the water from the reservoir rises into the tube ,n and then out through the small hole ,o to the carbide4 ,gas is immediately generated1 the pressure of which prevents further ingress of the water from the tube ,n1 and the generation of gas is suspended4 ,as the gas passes out through the valve at ,r the pressure decreases1 permitting the water to again rise in the tube and flow through ,o4 ,gas is again generated1 which at once exerts its pressure and cuts off the supply of water4 ,this is the automatic action by which water is brought in contact with the calcium carbide4 ,thus it will be observed that the use or escape of the gas regulates the generation by the simple device of the rise and fall of a water column4 ,there is a cap ,m screwed over the tube ,n4 ,this is used to deflect the course of the water downward1 so that the carbide in the lower part of the cartridge is first attacked4 ,there is a needle inside of cap ,m1 which can be used for cleaning the hole ,o4 ,when the gas is generated it passes through the filter ,d on its way to the burner through ,r4 ,this filter consists of a tube loosely packed with ordinary nonabsorbent cotton1 which should never cover the escape pipe leading to the valve ,r4 ,in passing through this cotton filter moisture and dust are removed from the gas4 ,in the latest model a felt filter is used instead of cotton4 ,illustration3 ,,fig4 #f4--,signal lantern generator4 ,the escape pipe ,f provides a means for the escape of gas generated and not used or generated more rapidly than consumed4 ,should an excess be generated1 it passes down through the tube ,f1 and1 finding its way through some small holes in the bottom of this tube1 escapes through the water seal and the opening at ,c4 ,it will be noted that if escaping gas at ,c should become accidentally lighted1 the flame can not strike back into the filter and cartridge because of the water seal4 ,the principal things to observe in the operation of this generator are the following3 7#a7 ,to see that the rubber plugs fit tightly into the openings of the cartridge4 7#b7 ,that the tube ,n1 the cap ,m1 and water hole ,o are not stopped up4 7#c7 ,that the cotton in the filter is changed frequently4 7#d7 ,that the stopcock ,r is closed before inserting the frame in the water4 ,if this latter instruction is not complied with1 it can be readily seen that the water will have free access to the carbide and excessive generation will occur4 ,when the charge is exhausted1 the entire cartridge is taken out and thrown away4 ,this eliminates the handling of carbide and the disagreeable task of cleaning out the residuum after the gas has been extracted4 ,connection is made from the stopcock ,r to the hose connection on the lantern proper1 and this is the passageway of the gas from the generator to the burner4 ,as soon as the stopcock is opened the water rises through the tube and flows to the carbide4 ,the advantage of the cartridge being submerged in the water is to reduce and absorb as much of the heat liberated by generation as is possible4 ,these lanterns have been tested up to a distance of #aj miles with the naked eye1 and under favorable conditions can be used over a range somewhat in excess of this4 ,with a #cj-power telescope the flash can be read at a distance of #cj miles4 ,operation and care4--,take the lamp and generator from the case by aid of the handle attached to the lamp2 screw the complete outfit on a heliograph tripod1 or stand the outfit on a level object2 remove the cover of generator1 to which is attached the flexible frame 7fig4 #i72 detach spring from the catch of the flexible frame2 tear off flaps from the ends of carbide cartridge 7or pry off small caps7 and attach the cartridge as shown in figure #i4 ,then attach to frame as shown in figure #aj1 being careful to see that both rubber plugs fit tightly into the holes in the cartridge2 fasten the latch of the spring over the metal catch2 close stopcock ,r on service pipe2 completely fill the outer can of generator with water1 the object being to have the generator level full of water when the lamp is in service1 then immerse the frame and cartridge1 pressing the top of the generator down tight4 ,in doing this the water will overflow the sides of the generator tank4 ,now connect by rubber tubing the stopcock with the gas inlet at the bottom of the lamps1 as shown in figure #d2 then 7#a7 open front door of the lamp1 7#b7 light a match1 7#c7 open stopcock1 and 7#d7 light the gas at the burner4 ,in doing this hold the key open4 ,in the new model the key and hose connection are on the side of bottom of lamp4 ,when the gas is ignited1 the lamp is ready for signaling1 and the key can be operated as is the ,morse telegraph instrument1 but of course not so rapidly4 ,in the event of the flame being too high when the key is closed1 adjustment can be made by loosening the set screw 7fig4 #d1 indicated by an arrow7 and adjusting the light by turning screw b4 ,when at the proper height1 tighten the set screw which locks the by-pass in its proper position4 ,in the new model this is accomplished by aid of the regulator by-pass valve at the left-hand side of bottom of lamp4 ,the lamp is properly adjusted when shipped and should not be changed unless absolutely necessary4 ,connect the rubber tube to the burner before opening the stopcock on the generator4 ,to recharge the generator1 take the frame and the old cartridge from the case1 throw away the old case and replace with a fresh one1 proceeding as before4 ,see that fresh water is put in the generator each time a new cartridge is used4 ,illustration3 ,,fig4 #g4 ,in the tube through which the service pipe passes is a felt filter for taking the dust out of the gas4 ,if the filter clogs1 unscrew the cap to which the service pipe is attached1 clean the felt1 or replace it with a new filter1 binding it in place by a stout thread or string4 ,if the burner of the lamp does not produce a perfectly flat flame it has become clogged and should be cleaned with the burner cleaner furnished1 or a new burner should be substituted1 care being taken to put a little white lead on the nipple1 if practicable1 so as to insure a tight joint4 ,in repacking the outfit in the case1 throw out the water and wipe the can and generator parts dry4 ,you can not be too careful to keep the apparatus clean4 ,this is especially true of the small pipe that passes up through the bottom of the cartridge1 with a cap over it4 ,the cap should always be screwed in place1 as its object is to prevent the water from squirting to the top of the cartridge4 ,illustration3 ,,fig4 #h4 ,illustration3 ,,fig4 #i4 ,the back of the lamp can be removed by turning the small thumbscrew on the top and drawing out the pin which holds the shell into which is fitted the lens4 ,it is not necessary to take the back out except to replace a lens1 as the latter can be cleaned by opening the front door4 ,if it is desirable to use the lamp as a hand lantern the flame can be turned on full by turning the button in a vertical position2 this locks the key open4 ,in the new model depress the key and lock it with the latch above the key4 ,one charge of calcium carbide will supply gas to burn about one hour with the light turned on full1 or for approximately three hours' signaling4 ,illustration3 ,,fig4 #aj4 ,if signaling is to be suspended for some hours1 empty the water out of the generator and close valve ,r4 ,the glass front can be replaced by taking out the wire spring4 ,the glass cuts should be mounted in a horizontal position and1 to prevent breaking1 should be protected from rain when the lamp is hot4 ,if a glass should be broken and an extra one is not available to replace it1 signaling can be continued by turning the flame on full and using the heliograph shutter1 a cap or piece of board in front of the lantern to obscure and reveal the flash4 ,without the protection of the cover the flame is easily blown out when turned low1 but will not be extinguished even in a strong wind if the gas is turned full on4 ,old model lamps are serially numbered from #a to #bjj1 inclusive2 the new model lamps are serially numbered from #bja upward4 ,powers and limitations of the acetylene signal lantern4--,as conditions are usually more uniform at night than in the daytime1 the signal lantern is probably the most reliable of all visual signaling outfits4 ,the advantages of this form of apparatus are its portability1 speed of operation1 and comparatively great range4 ,the principal disadvantages are due to the interference caused by rain1 fog1 and moonlight4 ,the speed attainable with the lantern is about the same as that attainable with the heliograph4 ,,rockets ,,and ,,shells4 ,two distinct kinds of rockets and shells are issued1 one of which is adapted to day and the other to night signaling4 ,shells and rockets of the amber smoke type with parachutes are used in the daytime1 while shells 7red and white7 and sequence rockets are used at night4 ,illustration3 ,,fig4 #aa4--,signaling rocket and accessories4 ,illustration3 ,,fig4 #ab4--,signaling shells4 ,description4--,the shells are all single shot and are fired from a #e-;inch portable mortar1 attaining a height of about #eej feet4 ,the report of explosion can be heard at varying distances up to #e miles1 depending on weather conditions4 ,the parachute attached to the smoke shell suspends a small light wooden tube which1 after ignition1 emits smoke for from four to six seconds4 ,the red and white shells1 on bursting1 discharge a shower of red and white fire which can be observed for some time1 in fact almost until the sparks fall to the ground4 ,rockets for both day and night signaling are equipped with parachutes4 ,the smoke rocket is of similar construction to the smoke shell4 ,the sequence rocket is so arranged at the base that threaded sections of combustible material burning either red or white can be attached to it4 ,rockets ascend about #gjj feet4 ,each rocket and shell is supplied in a cylindrical sealed tin can1 which also contains a port fire1 wind matches1 and for the rockets a stick in four sections4 ,on the outside of the can is a label designating the kind of shell or rocket therein contained4 ,these cans are easily opened by pulling a ring and require no special opening tool4 ,operation4--,in firing shells the mortar should be surrounded by earth or sand1 preferably placed in sacks4 ,the fuse for all shells is very rapid and should be ignited by attaching the port fire to a long stick4 ,all of the old type ,signal ,corps mortars1 originally designed to withstand a pressure of #a1jjj pounds per square inch1 and made of ordinary iron pipe1 are considered unsafe and should be immediately destroyed4 ,the new mortars1 recently made for the ,signal ,corps by the ,ordnance ,department1 are of cold-drawn steel having a tensile strength of #f1jjj pounds per square inch1 which is more than the maximum pressure for firing any of the ,signal ,corps bombs4 ,they are stamped ,signal ,corps1 ,u4 ,s4 ,a41 ,model #aijg1 or ,rocket ,gun1 ,watertown ,arsenal1 #aijg4 ,the sequence rocket is prepared for use by attaching red or white sections to the base in such a combination as to form letters of the alphabet which it is desired to use4 ,letters containing the same color in sequence are very difficult to read and should be avoided whenever possible4 ,if necessary to use them1 blank sections furnished for the purpose should be inserted between the units4 ,the base of the rocket will secure six units4 ,when rockets are to be fired the sticks must be firmly attached1 the rocket placed upright in a trough1 upon a frame1 or against a post4 ,if the fuse is beneath the paper covering the choke orifice1 the paper should be torn off and the rocket ignited by a port fire4 ,in the rockets now used the fuse extends through the covering and can be lighted direct4 ,if the night be damp this fuse should be exposed only a moment before the rocket is fired4 ,if several rockets are to be fired in succession it is well to prepare them all at the same time1 and to have them all stood upright1 but each separated from the other at a distance of at least #f feet1 else one may ignite the other accidentally4 ,in firing for chronosemic signals1 one rocket ought to be kept ready upon the frame and in reserve1 to be fired in place of one that fails4 ,if a rocket misses fire it is to be taken from the stand and laid on the ground4 ,its place is at once supplied by a similar rocket1 fired in its stead4 ,the failing rocket is laid on the ground pointed away from the station in order that if it has only hung fire and should afterwards ignite it may not disarrange the signal shown or injure any one of the party4 ,if the wind blows freshly the rocket to be fired should be inclined slightly against the wind4 ,signal rockets and shells are furnished in sealed cans and should not be removed therefrom until ready for use4 ,strict economy should be observed in the use of these articles and on no account should they be used for purposes of display4 ,employment4--,rockets and shells are especially valuable in making preconcerted or emergency signals4 ,on account of the great amount of ammunition required it is impracticable to spell out messages with them4 ,these articles should be supplied to outposts1 detached stations1 etc41 to be used for signaling the approach of the enemy or the happening of unexpected events1 the necessity for promptly knowing which is important4 ,,the ,,semaphore4 ,if signal stations are to be permanently occupied1 and it is impracticable to electrically connect them1 communication may be facilitated by erecting semaphores4 ,semaphores1 while primarily used for day signaling1 can be advantageously used at night by attaching lights to the arms4 ,the navy semaphore consists of four arms pivoted at the ends1 three on one side of the upright1 or pole1 and one on the other side4 ,these arms have three positions3 ,horizontal2 upward at an angle of #de to the horizontal2 downward at an angle of #de to the horizontal4 ,full instructions for the operation of the semaphore1 and also for the use of balls1 cones1 drums1 pennants1 and whefts as distant signals1 are given in the ,international ,code of ,signals4 ,,the ,,searchlight4 ,the electric searchlight1 when available1 can often be successfully employed for night signaling1 frequently affording efficient means of communication between ships and shore stations1 when wireless working is impracticable4 ,this system of visual signaling is practicable and especially valuable where the stations are1 on account of the terrain1 not intervisible4 ,methods of employment4--,in signaling with the searchlight the usual method of handling the shaft or beam is identical with that employed with the flag4 ,in the first position the beam is shown vertically1 while motions to the right1 the left1 and directly serve to indicate the elements of the alphabet4 ,chronosemic signals may also be used in searchlight signaling1 the shaft of light being directed intermittently on some conspicuous object1 such as a cloud1 balloon1 or high mountain top4 ,,coston ,,signals4 ,these signals are pyrotechnic compositions which burn with great intensity of light and color4 ,the colors red1 white1 and green are found best suited for signaling4 ,the signals are prepared in the form of cartridges and are burned from a holder4 ,the colors burned may indicate the elements of any alphabet1 or such other special signals as may be desired4 ,,very',s ,,night ,,signals4 ,the ,very system employs projected red1 white1 and green stars1 which are shot from pistols held in the hand4 ,description4--,the ,very pistol is a breechloading1 single-shot pistol with an #h-;inch steel barrel chambered to receive a #ab-;gauge commercial shotgun shell4 ,brass shells are used and are packed in boxes colored to indicate the character of stars employed in loading4 ,the color of the star fired may indicate an element of any alphabet or any special signal which may be desired4 ,the stars rise to a height of about #bjj feet and remain visible for some time4 ,,the ,,ardois ,,system4 ,the ,ardois system is a special system of night signaling designed to utilize combinations of red and white signal lights in forming the elements of any desired alphabet4 ,four signal lamps capable of displaying either red or white lights are attached at convenient intervals to a vertical cable or staff rigged between the top of a mast and the deck1 if on shipboard1 or the ground1 if on shore4 ,illumination is furnished by electrical means and any desired combination of lights is automatically obtainable by operating a keyboard4 ,this system is valuable on vessels or at permanent shore stations1 but the great expense of installation precludes its general use4 ,wiring diagrams and technical instructions relative to this apparatus are in all cases furnished when the same is issued4 ,illustration3 ,,fig4 #ac4--,the ,very pistol4 ,,sound ,,signals4 ,when recourse to any method of sight signals can not be had on account of weather conditions or lack of suitable apparatus1 sound signals may often be advantageously used4 ,the commoner means of furnishing sound signals are the horn and the whistle1 though many other kinds of apparatus are practicable4 ,the necessary elements of any system can be indicated by one short1 two shorts1 and a long blast4 ,the advantage of this system of signaling is that it can be used in any kind of weather1 both in daytime and at night4 ,on the other hand1 sound signals are generally more difficult to read than sight signals and tend to disclose the presence of stations to hostile forces4 ,,improvised ,,signaling ,,methods4 ,the object of this chapter has been to describe only the standard visual signaling equipment issued and generally utilized4 ,besides the methods detailed1 there are many others which may be successfully employed by the ingenious signalman when the necessity for them arise4 ,the use of any means of transmitting signals whatever is justifiable when for any reason the regular apparatus is not available4 ,special conventional scout signals are given in paragraph #hb1 ,field ,service ,regulations4 ,in the field many instances will occur where it will be necessary to transmit information rapidly without recourse to the authorized equipment4 ,this will be especially true of outposts1 detached stations1 patrols1 and other small bodies of troops1 and it will devolve upon individual commanders to improvise methods of signaling best suited to the occasion and the conveniences at hand4 ,,chapter ,,iii4 ,,alphabets ,,or ,,systems ,,of ,,signals4 ,,signal ,,alphabets4 ,,american ,,continental ,,army ,,and ,letters-- ,,morse4 ,,morse4 ,,navy4 ,a -- -- #bb ,b -- -- #baab ,c -- -- #aba ,d -- -- #bbb ,e #ab ,f -- -- #bbba ,g -- -- -- -- #bbaa ,h #abb ,i #a ,j -- -- -- -- -- #aabb ,k -- -- -- -- #baba ,l ---- -- #bba ,m -- -- -- -- #abba ,n -- -- #aa ,o -- -- -- #ba ,p -- -- #abab ,q -- -- -- -- #abaa ,r -- #baa ,s #bab ,t -- -- #b ,u -- -- #aab ,v -- -- #abbb ,w -- -- -- -- #aaba ,x -- -- -- #babb ,y -- -- -- #aaa ,z -- -- #bbbb tion #aaab ,numerals-- ,,american ,,continental ,,army ,,and ,,morse4 ,,morse4 ,,navy4 #a -- -- -- -- -- -- #aaaa #b -- -- -- -- #bbbb #c -- -- -- #aaab #d -- -- #bbba #e -- -- -- #aabb #f -- #bbaa #g -- -- -- -- #abbb #h -- -- -- -- #baaa #i -- -- -- -- -- -- #abba #j ------ -- -- -- -- -- #baab ,punctuation-- 4 ,period -- -- 3 ,colon ,ko -- -- -- 2 ,semicolon ,si -- -- -- 1 ,comma -- -- -- -- --- 8 ,interrogation -- -- -- -- 6 ,exclamation -- -- -- -- -- -- -- ,fraction line - - ,hyphen ,hx -- -- ' ,apostrophe -- -- -- -- ,pound ,sterling -- -- 77 ,parenthesis ,pn -- -- -- -- ,quotation marks ,qn -- -- -- -- ,paragraph -- -- -- -- ,brackets ,bn ,dollar mark ,sx ,dash ,dx ,underline ,ux ,the following abbreviations1 conventional signals1 and code calls are authorized in visual signaling3 ,,abbreviations4 a after4 b before4 c can4 h have4 n not4 r are4 t the4 u you4 ur your4 w word4 wi with4 y yes4 ,,code ,,calls4 ,international ,code use ,,icu 7,navy7 telegraph dictionary use ,,tdu 7,navy7 geographical list use ,,glu 7,navy7 general signal use ,,gsu ,navy list use ,,nlu ,vessel's numbers use ,,vnu ,cipher ,a usea ,,cau ,cipher ,b usea ,,cbu ,cipher ,c usea ,,ccu ,,footnote3 a ,these calls are for preconcerted use in or with the navy4 ,although the use of but one alphabet is authorized in visual signaling in the ,u4 ,s4 ,army1 emergencies may arise where it may be imperative to use either the ,army and ,navy1 the ,continental ,morse1 or the ,american ,morse alphabet4 ,instructions for the use of either alphabet under such conditions are given4 ,,execution ,,of ,,signal ,,alphabets4 ,,the ,,army ,,and ,,navy ,,alphabet4 ,,signaling ,,with ,,flag ,,or ,,torch1 ,,hand ,,lantern1 ,,beam ,,of ,,searchlight1 ,,and ,,heliograph4 ,there is one position and three motions4 ,the position is with the flag or other appliance held vertically1 the signalman facing directly toward the station with which it is desired to communicate1 his body erect and feet sufficiently separated to insure stable equilibrium4 ,the first motion 7one or #a7 is to the right of the sender1 and will embrace an arc of #ij1 starting with the vertical and returning to it1 and will be made in a plane at right angles to the line connecting the two stations4 ,the second motion 7two or #b7 is a similar motion to the left of the sender4 ,the third motion 7front1 three1 or #c7 is downward directly in front of the sender and instantly returned upward to the first position4 ,the beam of searchlight will be ordinarily used exactly as the flag1 the first position being a vertical one4 ,to use the torch or hand lantern1 a footlight must be used as a point of reference to the motion4 ,the lantern is more conveniently swung out upward to the right of the footlight for #a1 to the left for #b1 and raised vertically for #c4 ,in using the heliograph1 the first position is to turn a steady flash on the receiving station4 ,the signals are made by short and long flashes4 ,use short flashes for #a1 two short flashes in quick succession for #b1 and a long1 steady flash for #c4 ,the elements for a letter should be slightly longer than in sound signals4 ,each word1 abbreviation1 or conventional signal is followed by #c4 ,the full address of a message is considered as one sentence and will be followed by the signal #cc4 ,the signal to indicate that cipher follows and cipher ends is with the flag and torch ,,xc#c1 and with other methods1 except the ,international ,code1 by ,,xc4 ,it will always precede and follow a cipher message or such part of a plain text message as is enciphered4 ,the following conventional signals are authorized in the use of the army and navy alphabet3 ,end of a word #c ,end of a sentence #cc ,end of a message #ccc ,numerals follow 7or7 numerals end xx#c ,signature follows sig4 #c ,error #ab #ab #c ,acknowledgment 7or7 ,i understand #bb #bb #c ,cease signaling #bb #bb #bb #ccc ,cipher follows 7or7 cipher ends #babb #aba #c ,wait a moment #aaaa #c ,repeat after 7word7 #aba #aba #c #bb #c 7word7 ,repeat last word #aba #aba #cc ,repeat last message #aba #aba #aba #ccc ,move a little to the right #baa #baa #c ,move a little to the left #bba #bba #c ,signal faster #bbab #c ,,the ,,morse ,,alphabets4 ,,to ,,signal ,,with ,,the ,,flag1 ,,torch1 ,,hand ,,lantern1 ,,or ,,beam ,,of ,,searchlight4 ,the dot is made by a motion to the right of the sender embracing an arc of #ij1 starting from the vertical and returning to it1 in a plane at right angles to the line connecting the two stations4 ,the dash is made by a similar motion to the left4 ,the space which occurs only between dots is made by prolonging the signal for the last dot for an interval of time equal to the time of an additional dot1 the staff of the flag1 the beam of the searchlight1 etc41 being maintained in a horizontal position for the time specified4 ,the signal so made would therefore represent a dot and space4 ,the letter ,c is accordingly made thus3 ,right1 right prolonged1 right4 ,the long dash 7,l7 is distinguished from the short dash 7t7 by prolonging the signal to the left for a period of time equal to one dot4 ,the long dash representing naught is similarly made by prolonging the signal to the left for a period of time equal to two dots4 ,the front signal is made by lowering the flag from the vertical position to the front and immediately returning it to the vertical position4 ,a slight pause is made between each signal4 ,the following conventional signals are authorized1 using the ,morse alphabets3 ,end of word one front4 ,end of sentence two fronts4 ,end of message three fronts4 ,,to ,,signal ,,with ,,the ,,heliograph ,,or ,,flash ,,lantern4 ,the dot is made by pressing down the key of the shutter and immediately releasing the same4 ,the short dash is made by pressing down the key and holding it down for a period equal to two dots4 ,the long dash 7,l7 is made by holding down the key for a period equal to three dots while the longer dash 7naught7 requires the key to be held down for a period equal to four dots4 ,the space is made on the heliograph as in ordinary telegraphy by the absence of any signals for a period equal to the time of one dot4 ,on the heliograph the letter ,c is made as follows3 ,short flash1 short flash1 interval1 short flash4 ,illustration3 ,fig4 #ad4 ,illustration3 ,fig4 #ae4 ,when the call of a station is acknowledged1 both stations will adjust each on the flash of the other4 ,when adjustments are satisfactory1 the station called will acknowledge and cut off its flash1 and the calling station will proceed with its message4 ,,international ,,code ,,of ,,signals4 ,description4--,by means of the ,international ,code of ,signals people of different nationalities may communicate with each other1 although neither party has knowledge of any language save his own native language4 ,the code is1 as its name indicates1 international1 and every seagoing vessel of every nation is equipped with its flags4 ,the ,code of ,signals contemplates the use of #bf flags 7figs4 #ad and #ae72 one for each letter of the alphabet and a code pennant4 ,complete instructions relative to the use of this code are contained in a book issued by the ,hydrographic ,office1 ,navy ,department1 and known as the ,the ,international ,code of ,signals4 ,in using this system the signals are displayed by hoisting combinations of two1 three1 or four flags4 ,all possible combinations represent words1 expressions1 or phrases1 which may be found in the ,international ,code of ,signals1 referred to above4 ,two-arm semaphore4--,this system is frequently used by the ,united ,states ,navy1 the following instructions covering the use of the system3 #a4 ,to communicate with a station3 ,face the station and wave the flags over the head to attract attention1 making at frequent intervals the call letter of the station4 ,when the station called is ready to receive the message1 it answers by displaying its own call letter until the sender makes the alphabetical or numeral1 as the case may be4 ,then proceed with the message4 ,at the end of each word bring the flags across the lower part of the body4 #b4 ,to call a ship3 ,hoist ,international ,code letter ,j and make code letter of ship2 then proceed as in article #a4 #c4 ,to make a general semaphore signal3 ,hoist cornet2 all ships answer by answering pennant2 then make signal4 #d4 ,at the end of the message extend the arms horizontally and wave the flags until the receiver answers in the same manner1 showing that the message is understood4 ,should the receiver miss a word1 he signifies the fact by waving the flag over his head4 ,the sender will then cease signaling and wave his flags similarly to show that he understands4 ,the receiver then makes repeat last word1 or whatever he wishes to say4 ,should the sender make a mistake1 he will make the error signal until answered by the receiver with the same signal4 ,he then proceeds with the message4 ,,the ,,ardois ,,system4 ,in using this system in connection with the ,army and ,navy ,code1 the red lamp indicates #a and the white lamp #b4 ,four lamps are placed on a vertical staff and electrically illuminated to indicate the numerals of the ,myer ,code1 which represents the letters of the alphabet4 ,for instance1 white-white1 or #bb1 represents the letter ,a1 and white-red-red-white1 or #baab1 represents the letter ,b1 etc4 ,in this system the lights indicating the letters of the alphabet are read from the top downward4 ,when the lamps are placed horizontally1 they are read from the sender's right to his left1 and consequently from the receiver's left to his right4 ,when the letters of the alphabet are to be used to indicate the meaning set opposite them in the following tabulation1 the upper light of the display is pulsated4 ,this is effected by means of a special pulsating key4 ,special signification is not given ,i and ,t1 they being represented by a single lamp4 ---------------------------------------- ----------- ,steady ,upper light pulsated4 display4 ---------------------------------------- ----------- ,a ,cipher ,a use4 ,b #j 7naught74 ,c ,repeat 7following rule for conventional signals under wigwag code74 ,d ,telegraphic dictionary use4 ,e ,error4 ,f #d4 ,g #f4 ,h ,compass signals use4 ,i ,j #e4 ,k ,negative4 ,l ,geographical list use4 ,m #i4 ,n ,cipher ,b use4 ,o ,cipher ,c use4 ,p ,affirmative4 ,q ,interrogatory4 ,r ,international code use4 ,s ,general signals use4 ,t ,u ,navy list use4 ,v #g4 ,w ,annulling4 ,x ,numerals4 ,y ,vessels' number use4 ,z #b4 ,letters #c4 ,code call #h4 ,interval ,boat signals use4 ---------------------------------------- ----------- ,before numerals are made1 the distinctive signal for numerals ,x is shown and the upper light is pulsated1 which serves still further to distinguish them from letters4 ,the resumption of letters after using numerals will be indicated by the upper light being no longer pulsated1 but the display letters 7#c7 will be turned on as an additional indication4 ,the acknowledgment of the correct receipt of a message will be indicated by the letter ,r4 ,if the message has not been fully received1 or if it is not understood1 indication thereof will be made by signaling the letter ,g4 ,the end of a word is indicated by #bbab4 ,,coston ,,signals4 ,letters of the army and navy alphabet may be represented at night by ,coston lights1 port fires1 or other colored pyrotechnical lights by displaying the red for one and the white for two4 ,in using the ,morse alphabet the red represents the dot and the white the dash4 ,coston signals and other similar lights are best suited for preconcerted signals4 ,,very',s ,,night ,,signals4 ,the navy signal book is used1 to which the following explanation refers3 ,the letter ,r stands for red and the letter ,g for green1 and each letter designates a separate star or cartridge4 ,bracketed stars are a pair of different colors1 discharged together from two pistols4 ,the system is based on the ,army and ,navy ,code1 red representing #a and green #b4 #a--,,rrrr4 #b--;,,gggg4 #c--,,rrrg4 #d--;,,gggr4 #e--,,rrgg4 #f--;,,ggrr4 #g--,,rggg4 #h--;,,grrr4 #i--,,rggr4 #aj--;,,grrrg4 ,affirmative1 or ,yes ,,rgrg ,negative1 or ,no ,,grgr ,numeral ,,grgg ,interrogatory ,,rgrr ,annulling ,,rrgr ,divisional point1 date1 designator1 or interval ,,ggrg ,r ,telegraphic dictionary1 bracketed4 ,g ,r ,geographical list1 followed by a rocket4 ,g ,r ,boat signals1 rocket followed by ,g ,r ,r ,navy list ,g ,g ,general call1 rocket followed by ,g4 ,message call1 ,g without the rocket4 ,the squadron1 division1 section1 or ship's call1 the number of squadron1 division1 section1 or ship4 ,answering1 or ,i understand ,r ,repeating1 or ,i do not understand ,g ,danger or distress1 ,r repeated several times in quick succession4 ,,rocket ,,signaling4 ,in general1 rockets and shells are best used in displaying preconcerted signals4 ,sequence rockets may also be used to display different colored lights in sequence to represent letters or numerals of the army and navy alphabet4 ,the method of attaching the sections in the base of the sequence rocket is described in ,chapter ,,iii4 ,in using sequence rockets in this manner1 the element #a of the army and navy alphabet is represented by a red star1 while a white star represents the element #b4 ,to send the letter ,a a rocket showing two white stars is sent up4 ,if ,b is to be sent1 a rocket showing white-red-red-white is discharged4 ,each star burns for four to six seconds1 and there is a slight interval between the visibility of each star4 ,between two or more stars of the same color1 as ,a1 ,n1 ,d1 dummies1 which show no light and carry the fire to the next star to be ignited1 are employed4 ,in the preparation of codes for signals with rockets or bombs there should always be arranged a preparatory signal which means ,are you ready8 etc41 and an answering signal1 which means ,repeat your last signal1 etc41 a signal annul1 which means ,disregard last signal1 and a signal to signify the correct receipt of the complete message1 or ,signal seen and understood4 ,illustration3 ,,two-,,arm ,,semaphore ,,alphabet1 ,u4 ,s4 ,,navy4 ,illustration ,illustration ,,conventional ,,signals4 ,end of word see instructions4 ,end of message see instructions4 ,error see instructions4 ,repeat last word ,c1 'end of word'1 once4 ,repeat last message ,c1 'end of word'1 #c times4 ,use paper and pencil ,p1 'end of word'1 twice4 ,,abbreviations4 ,a end of word after ,b before ,c can ,h have ,n not ,r are ,t the ,u you ,,ur your ,w word ,,wi with ,y yes ,,pg permission granted ,,ng permission not granted ,,xx numerals follow ,illustration3 ,,summary ,,of ,,signals1 ,,army ,,and ,,navy ,,alphabet4 ,,chapter ,,iv4 ,,the ,,field ,,message4 ,definition4--,the term field message is applied to all messages sent over field lines of information4 ,all field messages for transmission over field lines of information by electrical or visual means should be plainly written by the sender on the blank forms in the ,united ,states ,army ,field ,message ,book4 ,the practice of verbally delivering telegrams to enlisted men for transmission should invariably be discouraged4 ,in framing telegrams1 all words not important to the sense will be omitted4 ,the last name of the officer addressed1 or his title1 and the last name of the sender are generally sufficient4 7,paragraph #aaih1 ,army ,regulations47 ,the blank form4--,the ,united ,states ,army ,field ,message ,book issued by the ,signal ,corps is #d-e_/h inches wide by #f inches long1 and contains #dj message blanks with duplicate tissue sheets and two sheets of carbon paper4 ,the message is written on the yellow sheet1 which can be torn out for delivery4 ,the carbon sheet is attached to the book1 and contrary to the custom in most carbon duplicating books1 is placed under the tissue sheet when a message is being written4 ,when not being used1 the carbon sheet should invariably be kept in the back of the book4 ,when the upper carbon sheet has become worn out1 it should be torn out and the second carbon sheet used instead4 ,the blank form is shown in figure #af4 ,the back of the blank is ruled in squares and provided with scales for use in making sketches4 ,illustration3 ---------------------------------------- ------------------------------- ,no4 ,sent by ,time ,rec'd ,u4 ,s4 ,,army ,,field ,,message4 #a ,k ,mo #a4ae by ,time ,check ,a4 ,m4 ,these spaces for ,signal ,operators only ---------------------------------------- ----------------------------------- ,communicated by ,name of sending detachment ,,buzzer1 ,,phone1 ,,telegraph1 ,from,headquarters #ast ,corps1 ,,wireless1 ,,lantern1 ,,helio1 ,,flag1 ,,cyclist1 ,,foot ,,messenger1 ,location of sending detachment ,,mounted ,,messenger4 ,at,taylors ,school ,house1 ,kansas 7,underscore means used7 ,date,may #a1 #aiji;,hour#ab4de ,p4 ,m4,no4 ------------------------------- ,to ,signals ,platte ,city1 ,mo4 ,request ten miles buzzer wire be sent here quick ,jones ,received ,,fig4 #af4 ,writing the message4--,in writing the message the name of the sending detachment should appear after the heading from on the upper line1 as from ,headquarters #ast ,brigade1 while the location of the sender should appear on the second line after the heading at4 ,the heading hour on the third line should show the hour the message was written and not the hour the message was transmitted4 ,the heading received at the bottom of the page is filled in by the addressee and shows the time of the receipt of the message by him4 ,,instructions ,,to ,,operators4 ,use of message blank4--,the field message blank will be used for field messages both sent and received4 ,duties of sending operators4--,the sending operator will enter the time when the message is handed him for transmission in the left-hand corner at the bottom of the blank opposite the word ,received4 ,he will enter in the proper places1 at the head of the blank1 the number of the message1 the call letter of his station1 with his personal signal1 the check 7number of words or groups of cipher contained in message1 counting address and signature71 and1 after ,,ok has been received1 he will enter the time the message was sent1 and the call letter of the receiving station1 with the personal signal of the receiving operator4 ,order of transmission4--,to transmit a message1 the operator will send3 7#a7 ,the number of message and call letter of his station2 7#b7 his personal signal2 7#c7 the check2 7#d7 fm followed by name of sending detachment2 7#e7 at followed by location of sending detachment and date2 7#f7 ,ho followed by hour 7a4 m4 or p4 m47 message was written2 7#g7 address in full2 7#h7 period1 7 -- -- 72 7#i7 body of message2 7#aj7 sig 7signature follows72 7#aa7 signature4 ,duties of receiving operators4--,the receiving operator will add to the message received1 the month1 date1 and year1 and omit the sig1 fm1 and at1 and1 after satisfying himself that the check and number of words correspond will give ,,ok followed by the call letter of his station and his own personal signal4 ,he will then enter in the proper places1 at the head of the blank1 the call letter of his own station1 with his personal signal and the time the message was received4 ,communications confidential4--,communications transmitted by telegraph or signals are always confidential and will only be revealed to those officially entitled to receive them4 ,checking the message4--,in preparing the check of the message1 all words and figures written in the address1 body of the message1 and the signature will be counted4 ,in counting the check of a message1 all words1 whether in plain ,english1 code1 or cipher1 pronounceable or unpronounceable1 or initial letters1 will be counted each as one word4 ,the abbreviations for the names of places1 cities1 towns1 villages1 ,states1 ,territories1 and ,provinces1 will be counted as if written in full4 ,in the names of towns1 counties1 countries1 or ,states1 all of the words will be counted4 ,abbreviations of weights and measures in common use1 and cardinal points of the compass1 will be counted each as one word4 ,to prevent liability to error1 numbers and amounts should be written in words1 and when not so written1 the receiving operator will request that it be done4 ,if the writer declines to write the amounts in words1 the message will be accepted as written1 and each figure will be counted as one word4 ,figures1 decimal points1 and bars of division1 and letters will be counted each separately as one word4 ,in ordinal numbers1 the affixes1 st1 d1 nd1 rd1 and th1 will each be counted as one word4 ,in transmitting the telegram shown in figure #af1 the following would be sent by the operator3 ,no #a ,k ,mo ,,ck #ad ,,ob fm ,headquarters #ast ,corps at ,taylor's ,school ,house ,kan #a ho #abde ,,pm to ,signals ,platte ,city ,mo4 ,request ten miles buzzer wire be sent here quick sig ,jones ,,chapter ,v4 ,,the ,,signal ,,station4 ,,location ,,of ,,stations4 ,in field operations tactical considerations will usually prescribe within certain limits the number and general location of signal stations4 ,the general directions for deployment being given1 the signalman will be called upon to demonstrate his skill in the selection of particular locations most conducive to the efficient service of information4 ,illustration3 ,,fig4 #ag4--;,field signal station4 ,general considerations4--,considering all things1 the best location for a signal station is one which affords maximum visibility and at the same time minimum exposure to hostile observation4 ,these conditions1 apparently paradoxical1 can be more or less reconciled by the exercise of ingenuity on the part of the signalist4 ,a good theoretical knowledge of the special requisites of signal sites1 together with the ability to apply it to the conditions arising in any given case1 will result in securing the best obtainable locations4 ,the first essential of the signal station is visibility1 the second being that of concealment from hostile observation4 ,in acquiring a mean between conflicting requirements1 the following special considerations in the selection of stations should be considered4 ,backgrounds4--,backgrounds are important factors in the selection of signaling sites4 ,sky backgrounds are desirable as affording strong contrast and are therefore conducive to celerity in the transmission of signals4 ,they are rare and can only be secured when stations are located on the exact crest of ridges1 on mountain peaks1 or on lands which bound the horizon of view from the other stations4 ,stations with sky backgrounds1 while affording the best facilities for transmission1 are little adapted to the requirement of secrecy4 ,dark backgrounds are far more common and more easily obtainable than sky exposures4 ,they afford the maximum means of concealment from hostile observation1 but materially reduce the range1 speed1 and accuracy of signal transmission4 ,mixed or broken backgrounds are those which display varied colors behind the signals4 ,backgrounds of this description do not accord with either of the essential requirements of the signal station and should be avoided whenever possible4 ,in general1 sky backgrounds should always be selected for signal stations when conditions are such that the requirement of secrecy can be dispensed with2 if1 on the other hand1 there is reason to fear that the signals may be intercepted by the enemy1 dark backgrounds should invariably be chosen1 even though the disadvantages they impose1 render them less desirable visually4 ,azimuth of stations4--,the azimuth of signal stations should1 if possible1 be such that the visual lines of information should intersect the vertical plane through the apparent course of the sun1 at a considerable angle4 ,stations located so as to be unavoidably viewed from these directions during portions of the day are very liable to appear enveloped in a haze1 and telescopes1 if turned upon them1 are filled with dazzling light4 ,if the location of stations on or close to the sun line is unavoidable1 sites affording sky exposures should be chosen4 ,exposures of this kind obviate to a great extent the difficulty of sun haze and should be secured when this difficulty is encountered and it is impracticable to change the azimuth of the station4 ,altitude4--,the location of signal stations at high altitudes will tend to obviate difficulties arising from smoke1 haze1 and dust4 ,the undulation of the atmosphere noticeable on a hot summer's day is always less at a distance from the earth's surface1 and it is often practicable to read signals from a tree or housetop when they would be unintelligible from the ground4 ,this air undulation is less over spots well shaded than those exposed to the glare of the sun1 a fact that should be borne in mind in all telescopic examinations4 ,another reason for locating stations at high altitudes is because the cool night air1 the smoke and dust of the day1 and heavy mists lie close to the ground1 filling the depressions and lowlands1 while the higher points remain in view4 ,stations on high ground are then equally well adapted to day and night signaling4 ,sites and selections of this kind of terrain will not only often preclude the necessity for changes of location1 but also will allow the continuous working of the station when signals made from lower positions would be invisible4 ,in foggy or murky weather peaks and mountain tops are usually enveloped in mist1 and under these conditions stations should be situated on lower ground4 ,determination of background color4--,the color of the background of a station is that color against which the signals appear to be displayed when viewed from the distant station4 ,having chosen a point entirely in view of the station or stations to be communicated with1 and having fixed the exact position of the signaling apparatus1 the color of the background should be determined as carefully as conditions of terrain will permit4 ,if the elevation of the distant station is without doubt greater than that of the home station it is safe to assume that the color of the background will be that of the objects directly around and behind it4 ,on the other hand1 if the distant station unquestionably occupies the lower position1 a sky exposure will usually result4 ,in locating stations it is very difficult1 if not impossible1 especially at long ranges1 to determine the color of the background as viewed from the distant station when the stations are approximately on the same level4 ,this can only be done by proceeding in front of the home station and taking such a position that it can be viewed with the eye on the line of sight between the stations4 ,the telescope should be established over the initial point of the home stations and directed on the distant station4 ,the observer for background should proceed to a point where his head is in the center of the field of the telescope4 ,looking back at the home station from this point1 the color of the objects about and just behind the initial point will be the color of the background4 ,the correct determination of background color from the vicinity of home stations is usually difficult and unsatisfactory1 and it is considered the best method to establish communication with the distant station by simultaneously using several kinds of signaling apparatus1 that kind producing the most intelligible signals being retained for continued use4 ,choice of apparatus4--,sunlight conditions permitting1 the heliograph will ordinarily be used for day signaling on account of the advantages of the great range and speed afforded by it4 ,when its use is prohibited by weather conditions1 the flag will be substituted for it4 ,the white flag will be used against dark and the red against sky or broken backgrounds4 ,the distant station is the better judge as to which color flag is best suited to given conditions and the color indicated by it should invariably be used4 ,for night signaling1 the acetylene lantern is usually employed4 ,long-range night signaling should be done with the searchlight if available4 ,the employment of the semaphore1 in daytime1 and the ,ardois system1 at night1 will be confined to more or less permanent stations4 ,rockets1 shells1 night fires1 etc41 are only employed for special or emergency signals4 ,miscellaneous considerations4--,for various reasons stations should not be located at or near camp grounds4 ,these localities usually afford mixed backgrounds1 and the presence of dust and smoke and the interference caused by moving bodies of troops and trains will militate against the efficient transmission of signals4 ,stations located in vicinities of this kind are also subject to annoyance from noise and visits of unauthorized persons4 ,signal stations should be convenient for messenger service and hence as near commonly traveled roads as the physical contour of the country will permit4 ,locations for signal stations should be so selected that the visual lines do not cross traveled roads1 camps1 etc41 as dust and smoke in the daytime and lights at night are factors in determining the visibility of signals4 ,signal stations can if necessary be artificially concealed by erecting screens constructed of limbs of trees1 etc41 about the flanks and rear4 ,sheltered positions should be utilized in windy weather4 ,intervisibility table4--,the following table shows the extent of horizon for different heights above the sea level--that is1 it shows how far one can see an object which is itself at the level of the sea3 --------------------------------------- ,distance ,height of the eye above sea in statute level4 miles4 --------------------------------------- #aj feet #d #ae feet #e #bj feet #f #cj feet #g #dj feet #h #ej feet #i #fj feet #aj #gj feet #aa #he feet #ab #ajj feet #ac #aae feet #ad #acj feet #ae #aej feet #af #bjj feet #ah #bcj feet #bj #cjj feet #bc #cej feet #be #ejj feet #cj #gjj feet #ce #ijj feet #dj --------------------------------------- ,a formula to determine approximately the limits of visibility from a given height is as follows3 ,the square root of the height of the station in feet multiplied by #a4bf equals the distance in miles at which the signal is visible4 ,hence1 an observer whose eye is #cj feet above the sea can distinguish an object #g miles distant1 provided it is at the sea level2 but if the object is itself #ae feet above the sea he can make it out #g #e #ab miles off4 ,,finding ,a ,,station4 ,to find a signalman near any known station1 note with the unaided eye some prominent landmark near which the looked-for person or object is supposed to be1 and direct the telescope upon the place1 as sight is taken over a gun barrel1 covering the object2 if the eye is now placed at the eyeglass of the telescope1 the prominent or directing landmark will be found in the field of view4 ,it will be easy then to scale the country near the marker until the signalman is found4 ,this method is often necessary at night1 when only a point of light is seen far off through the darkness1 and the telescope must be turned upon it4 ,when the compass bearing of the object sought for is known1 the telescope may be aligned by a line drawn with the proper compass bearing4 ,commencing then with the view at the horizon1 the telescope is slowly moved from side to side1 taking in fresh fields of view each time a little nearer to the observer1 until the whole country shall have been observed from the horizon to quite near the station4 ,when the general direction only of the object can be given and it is sought for1 the whole landscape in that direction to the horizon should be divided into sections by imaginary lines1 the limits of these sections being bounded between visible landmarks through which the bounding lines are supposed to pass4 ,each section should be scrutinized little by little until the glass has been passed over every spot4 ,such search will seldom fail to be successful4 ,the magnetic bearings of all stations with which another station has worked should be carefully noted and made matter of record in the office directly concerned1 so that advantageous use may be made of this data4 ,in addition1 guide lines may be established by driving two stakes firmly into the ground and close to each other4 ,a prolongation of a line through the center of one post and marked on the adjacent one will strike the distant station4 ,under each line should be written the name of the station which it marks4 ,signalers upon permanent or semipermanent stations will examine1 from time to time1 every prominent point within signal distance1 to see if communication is attempted therefrom4 ,attempts to attract the attention of a known station1 in order to be successful1 must be persistent4 ,they should never be abandoned until every device has been exhausted1 and they should be renewed and continued at different hours of the day and night4 ,it must be remembered that efforts which have failed because the observer's attention has been drawn in another direction may at any other moment be successful if the observing glass chances to bear on the calling signals4 ,during the whole time that signals are being made to attract attention the calling station must watch closely with the telescope the station called4 ,the watch should not be relaxed until communication is established or the station ordered abandoned4 ,illustration3 ,,fig4 #ah4--,signal ,corps heliograph station4 ,,operation ,,of ,,stations4 ,personnel4--,at signal stations where continued operation is required at least a squad or set of fours is required4 ,physical and mental exhaustion always result from continuous signal duty1 and as alertness of mind and body is an indispensable factor in the prevention of errors1 two reliefs of signalmen should be furnished each station whenever practicable4 ,the senior officer or enlisted man is in charge of the station and is responsible for efficiency and discipline4 ,he will require from each man a strict and entire attention to his own immediate duties1 and permit no conversation that will distract the men at work4 ,he will be careful not to allow persons to loiter about the station or within the hearing of the words called out to the signaler4 ,the assignment of men should be such that a continuous watch for signals is kept and the responsibility for neglect to promptly answer calls determined4 ,of the station men1 one is the sender1 whose duty it is to transmit all signals to contiguous stations4 ,another1 the receiver1 attends the telescope and reads and calls off the signals displayed at the distant station4 ,a third man acts as recorder1 alternately calling off the outgoing message to the sender or transcribing the incoming message repeated by the receiver4 ,calls and personal signals4--,each station will be assigned a call consisting of one or two letters4 ,each and every operator will also have a personal signal of like character4 ,station calls or personal signals when once given or assumed will not be changed except by order of higher authority4 ,every station should at all times have on hand a list of all calls and personal signals liable to be encountered in station working4 ,the general call suited to attract the attention of any station whose regular call is unknown will always be a signal represented by the letter ,a in the ,morse or the letter ,e of the ,army and ,navy ,code4 ,opening communication4--,to open communication with any distant station whose call is known1 signal the call repeatedly1 occasionally signing the call of the home station4 ,if the regular call of the station sought is unknown the general call above prescribed should be used4 ,as soon as the call is observed the called station will acknowledge receipt by ii ii1 or ,i understand1 signing thereafter its station call4 ,these preliminaries completed1 the stations are ready for working4 ,it is sometimes difficult to secure the attention of stations at unexpected hours4 ,the force may not be strong enough for an uninterrupted watch4 ,to provide1 so far as possible1 for this contingency1 it may be concerted that if communication is required at unusual time1 or is of pressing importance1 certain flags shall be displayed1 rockets discharged1 smokes shown1 or other attention-compelling signals used4 ,when a number of stations are in view from one station and it is desired to send a message to all or more than one station1 some preconcerted signal1 as a rocket1 a red light1 or some peculiar flag or torch signal1 should be designated as a signal for general attention4 ,upon noticing this signal all the called stations reply1 and then observe the calling station4 ,this plan is useful when two or more stations can1 at the same time1 read the signals from the one station1 and thus together receive any information to be transmitted from it4 ,when a signal station is to communicate with two or more stations1 a telescope should be firmly fixed bearing on each1 when practicable1 and so far apart that those communicating with one station will not disturb the other party4 ,commencing the message4--,every message is invariably commenced by the signal ,hr or ,anr4 ,sometimes at the commencement of communication a preface will be sent in order to give some preparatory information to the receiving station regarding the number or character of messages about to be sent4 ,for example1 ,hr #h1 means ,i have eight for you or ,hr ck #cjj means a three hundred word message follows4 ,sending and receiving4--,before the commencement of a message1 care should be taken that all the letters and characters thereof are entirely and correctly understood by the signalman whose duty it is to call the same to the sending operator4 ,the message is read off by the reader1 who first calls off a word and then spells it out letter by letter4 ,the reader should observe the signals of the operator and invite his attention to any apparent errors4 ,when the last letter of a word is announced this fact will be communicated to the sending operator4 ,at the receiving station the man at the telescope will call off each letter as received and not wait until the completion of a word4 ,on reaching the end of a word announcement of this fact will be made to the recorder4 ,breaking4--,if the sending operator discovers that he has made an error which will probably render the sense of the message unintelligible at the receiving station1 he will make the signal ,,bk and recommence the message1 beginning at the last word correctly sent4 ,when the receiving station fails for any reason to get correctly what is being sent1 the sending station is interrupted by the signal ,,ga1 followed by the last word correctly received4 ,the message will then be recommenced by the sending station at the point indicated4 ,discontinuance of transmission4--,when all the messages on file at any station have been sent the signal ,,nm in ,morse or ,cease signaling in the army and navy system1 according to which code is authorized1 will be the concluding signal of the sending station4 ,when a signal station is operated only during the daytime1 the signal ,,gn will be transmitted after all business filed up to the hour designated for closing has been dispatched4 ,acknowledgment of receipt4--,no message will be considered sent until receipt for the same has been acknowledged4 ,this is effected by making either the ,i understand of the army and navy or the ,,ok of one of the ,morse systems1 depending upon the one authorized4 ,in every case the receiving operator's signal is signed after acknowledgment4 ,when a number of messages are continuously sent1 one acknowledgment for all will suffice and will be so understood4 ,in receiving messages nothing should be taken for granted and nothing considered as seen until it has been positively and clearly in view4 ,station records4--,records kept at field signal stations will be confined to original files of messages sent and carbon copies of messages received4 ,ordinarily the only available stationery will be the ,united ,states ,army ,field ,message ,book4 ,station records will be invariably preserved as part of the station equipment until orders for their disposition are given by higher authority4 ,whenever a station is in imminent danger of capture1 all records should be destroyed in the discretion and under the direction of the operator in charge4 ,formation of signals4--,make signals with regularity2 do not send one word rapidly1 the next slowly2 adopt such a rate of speed as can be read by the distant signaler without causing him to break frequently4 ,make a distinct pause between letters4 ,it is time gained to do so2 it is a loss of time and an annoyance to run letters together4 ,nothing so distinguishes the good from the indifferent operator1 visual or telegraph1 as this4 ,when signals are being made with a flag1 a fraction of a second will be ample4 ,in using the lantern or heliograph1 the pause between letters should be relative to the time of display of the elements1 longer than with the flag4 ,to prevent any entangling of the flag upon its staff1 skillful handling1 acquired by practice1 is necessary4 ,it is accomplished by making a scoop of the flag against the wind1 the movement describing an elongated figure #h1 thus 4 ,the motions should be made so as to display in the lateral waves the whole surface of the flag toward the point of observation4 ,in using the heliograph1 if the receiver sees that the sender's mirror needs adjustment1 he will turn on a steady flash until answered by a steady flash4 ,when the adjustment is satisfactory1 the receiver will cut off his flash and the sender will resume his message4 ,repeating the message4--,it may happen that very important messages received by signals must be verified by repeating back from the receiving station1 signal by signal1 each signal used by the sending station in conveying the message4 ,there can be no error in signals thus verified1 and the correct transmission of the message is made certain4 ,for such verification each signal must be repeated by the receiving station as soon as it is made at the sending station4 ,signal practice4--,full efficiency of the signaler can be maintained only through constant practice1 and those in charge of ,signal ,corps troops should see that sufficient practice be had to insure that accuracy and rapidity in handling messages which is so essential in time of war4 ,instruction should commence with the study of the principles of signaling and the theories of their general use1 and the pupil should be well grounded in this study before practice is begun4 ,he should so memorize the alphabets to be used that no letter combination will require thought to determine its meaning4 ,daily inspections should be made to insure that all signaling instruments1 appliances1 and materials are in readiness for instant use4 ,defects in the apparatus annoy the sender2 to a greater extent they annoy the person to whom the messages are imperfectly sent1 and delays result that may have serious consequences4 ,,chapter ,,vi4 ,,codes ,,and ,,ciphers4 ,a code is a list or collection of arbitrary words or groups of letters to each of which some ordinary word1 proper name1 phrase1 or sentence is assigned for meaning4 ,ciphers embrace all means whereby writings may be transcribed into occult terms4 ,all ciphers employ some distinct method for transcription1 which method is termed a key4 ,in practice the key is usually applied directly in enciphering and reversed in deciphering messages4 ,,codes ,,in ,,use4 ,the codes of the ,western ,union and ,postal ,telegraph companies are examples of well-known codes suited to general commercial use4 ,besides these1 many special codes have been formulated1 so as to embody technical expressions especially adapted to use in particular lines of industry4 ,the ,war ,department ,code is a military code adapted to the special needs of the military establishment in peace and war4 ,,employment ,,of ,,codes4 ,codes are primarily intended for economy1 but they may also be readily employed to secure secrecy4 ,when used solely for economy1 the coded message is said to be plain code2 that is1 the word or phrases of the message are coded by direct reference to their respective code equivalents4 ,thus plain code is readily translatable to anyone in possession of a code book4 ,when secrecy is desired1 some method of enciphering or key is employed in such a way that only persons in possession of it can in conjunction with the code book decipher it4 ,in such case the message is said to be in cipher code4 ,,cipher ,,code4 ,in all codes each expression and its equivalent in plain language is assigned a number4 ,these numbers usually commence at unity and increase consecutively to any desired figure4 ,messages may be enciphered by means of a key number or series of numbers4 ,an additive number1 say #ee additive1 requires that in enciphering a message1 the fifty-fifth word numerically greater than the proper code word shall be used2 if #ee subtractive is used1 the fifty-fifth word numerically smaller than the proper code word is to be used4 ,by agreement a single key number can be used alternately additive and subtractive1 that is1 first additive1 second subtractive1 third additive1 etc4 ,the key numbers are used over and over until the entire message is enciphered4 ,the key number can sometimes be expressed by a single word1 as1 for instance1 ,grant1 each letter having a value of tens in accordance with its position in the alphabet2 that is1 ,g1 the seventh letter equals #gj2 ,r equals #ahj2 ,a equals #aj2 ,n equals #adj2 and ,t equals #bjj4 ,or by preconcerted arrangement letters may represent units or hundreds4 ,security from translation by persons not having the key number is greater when the key numbers are used alternately additive and subtractive4 ,if a cipher key word is used1 it should be one of an odd number of letters1 as1 for instance1 ,jones1 the numbers corresponding to the positions of the letters in the alphabet4 ,the first number should be additive1 the second subtractive1 etc4 ,by this means the first letter of the key word is additive the first time it is used1 subtractive the second1 additive the third1 and so on4 ,in some instances the key number1 when added to or subtracted from the code number1 gives a resulting number exceeding the highest code number or less than unity4 ,in cases of this kind it should be remembered in enciphering that unity follows the highest code number in addition1 and that the highest code number follows unity in subtraction4 ,in deciphering a message the process of enciphering is reversed4 ,,the ,,war ,,department ,,code4 ,as previously stated1 the ,war ,department ,code is the technical military code and contains expressions numbered consecutively from #a to #fb1jjj4 ,all the code words are composed of #f letters1 which are so arranged that the vowels and consonants invariably alternate4 ,in the formation of code words the following #ac letters only are used1 viz1 ,a1 ,b1 ,d1 ,e1 ,f1 ,g1 ,i1 ,k1 ,m1 ,n1 ,s1 ,u1 and ,x4 ,the body of the code book is arranged as follows3 7a7 ,army list1 containing the name of every commissioned officer in the regular establishment4 7b7 ,military organizations1 giving all batteries1 companies1 troops1 etc4 7c7 ,military posts and stations1 covering ,alaska1 ,hawaii1 ,philippine ,islands1 ,porto ,rico1 and the ,united ,states4 7d7 ,united ,states naval stations and vessels4 7e7 ,geographical names4 7f7 ,miscellaneous tables as follows3 ,numerals4 ,arrivals and departures4 ,dates4 ,indorsements4 ,letter acknowledgments4 ,requisitions4 ,telegram acknowledgments4 ,mails1 shipments1 and transports4 ,blanks for future additions as they may be needed4 ,ranks and grades of officers and men in the ,army4 ,wireless stations of the ,army and ,navy4 7g7 ,alphabetical list of code expressions arranged conveniently for use4 ,when it is desired to transmit some word or expression not to be found in the code and no suitable synonym can be discovered the word or expression should be sent in plain language or spelled out by the equivalents for letters and endings to be found on page #ehi4 ,complete instructions for the use of the code either as a code or cipher are contained in the introductory pages of the book4 ,,cipher ,,code ,,in ,,field ,,work4 ,the use of cipher code in enciphering field messages will usually be practicable only between the several headquarters and other large stations supplied with code books4 ,this method1 too1 is prohibitive for urgent messages when the time of enciphering and deciphering is an important factor connected with delivery4 ,,field ,,ciphers4 ,description and use4--,field ciphers include all systems and the apparatus connected therewith which are ordinarily employed in enciphering and deciphering field messages4 ,field ciphers are intended for use when code books are not available1 and hence the employment of cipher code is precluded4 ,some methods of field cipher employ simple forms of apparatus1 while others require the use of no apparatus at all4 ,forms of field cipher4--,there are two general classes of field cipher4 ,the first class employs the transposition or reversal of the letters or words of a message according to some preconcerted rule as a means of secrecy4 ,the route cipher hereafter described is an example of this class4 ,the method used in ciphers of the second class consists in the substitution of certain letters or symbols for each of the individual letters composing the words of the message4 ,both classes of cipher can be rendered more efficient by a judicious use of inversions and by the concealment of terminations4 ,inversions4--,by the inversions of the whole or certain parts of messages1 according to some preconcerted arrangement1 the complications of cipher can be greatly increased4 ,if a message is to be inverted1 either as a whole or by clauses1 it should be inverted before the cipher letters are written over it4 ,messages may be further complicated by sending the letters of each word backward in various other prearranged combinations4 ,concealment of terminations4--,to evade the discovery of the key or keys employed1 it is most important that the termination of the words of a message should be concealed4 ,the best method to conceal the beginning1 and at the same time the termination of words1 is to divide them into arbitrary groups of four or five letters each4 ,this procedure will add immeasurably to the strength of the cipher and should in no way confuse one in possession of the key4 ,for instance1 the words sufficient time would be divided suff icie ntti me1 and such blind letters as may be agreed upon to fill the last two spaces of the last group4 ,all such artifices as this will surely delay a translator not in possession of the key4 ,,cipher ,,apparatus4 ,the cipher disk4--,the cipher disk is composed of two disks of cardboard1 leather1 or other material joined concentrically1 the upper disk revolving upon the lower4 ,the alphabet1 reading from left to right1 and such other signals1 numerals1 or combinations of letters1 as may be desired1 are printed around the circumference of the lower disk4 ,on the upper disk are printed the alphabet and such other signals1 numerals1 or combinations of letters as are printed on the lower disk4 ,on the lower disk they are printed from left to right1 while on the upper disk they are printed from right to left4 ,if it is desired to encipher a message1 the key letter or the first letter of the key word or words is set opposite ,a4 ,let us assume it to be ,j4 ,the cipher letters to be written are those opposite the text letter when the letter a on the upper disk is set opposite ,j on the lower disk4 ,for example1 ,send powder would be written rfwg uvngfs4 ,having a cipher disk as above described1 this mere transposition of letters would delay but a short time the deciphering of a message by one not knowing the key letter1 as it would be necessary only to place1 in turn1 opposite a each of the letters of the alphabet beginning with b and noting the letters opposite the enciphered letters4 ,but this simple disk can be used with a cipher word1 or preferably1 cipher words known only to the correspondents1 and it is entirely improbable that a message so enciphered could be deciphered in time to be of any value to the enemy4 ,using the key words permanent body to encipher the message ,reenforcements will reach you at daylight1 we would proceed as follows3 ,write out the message to be enciphered and above it write the key word or key words1 letter over letter1 thus3 ,,permanentbodypermanentbodypermanentb ,reenforcementswillreachyouatdaylight yanzvznlppkqfxijb,bpwanruqpeplomccwhmi ,now bring the a of the upper disk under the first letter of the key word on the lower disk1 in this case ,p4 ,the first letter of the message to be enciphered is ,r4 ,y is found to be the letter connected with ,r and it is put down as the first cipher letter4 ,the letter a is then brought under ,e1 which is the second letter of the key word4 ,e is to be enciphered and a is found to be the second cipher letter4 ,then bring a to ,r and the cipher letter will represent e1 the third text letter of the message4 ,proceed in this manner until the last letter of the cipher words is used1 and1 beginning again with the letter ,p1 so continue until all letters of the message have been enciphered4 ,divided into groups of four letters1 it will be as follows3 yanz vznl ppkq fxij bpwa nruq pepl omcc whmi4 ,illustration3 ,,fig4 #ai4--;,cipher disk4 ,to decipher the message1 reverse the proceedings above described2 thus the letter a on the upper disk is brought under the first letter of the key word ,p4 ,following these instructions1 we find the first cipher letter of the message2 a is then brought to the next letter of the key word4 ,in this case ,e is1 of course1 the next letter of the text4 ,r is the next letter in the key and a is brought over it4 ,the cipher letter n gives us the next text letter1 which is e1 and so on until the completion of the message4 ,if the letters of the key word or phrase are exhausted1 begin again with the first letter and so continue until the entire message is deciphered4 ,with a key word1 or1 preferably1 a key phrase of three or four words1 the deciphering of a message is extremely difficult4 ,in a military cipher message1 it may be desired to transmit numerals1 the spelling out of which would require considerable time4 ,this can be done by an arrangement of the cipher disk so that the numerals of which will appear in the same order as and follow the letters of the alphabet4 ,thus on the lower disk #a is placed opposite ,a2 #b opposite ,b2 #c opposite ,c2 #d opposite ,d2 #e1 #f1 #g1 #h1 #i1 and #j opposite ,e1 ,f1 ,g1 ,h1 ,i1 and ,j1 respectively4 ,on the upper disk the above numerals also appear1 beginning numeral #a opposite ,a2 #b opposite ,b1 etc41 #j being opposite ,j4 ,the arbitrary sign ,,xx will be used to indicate numerals follow and numerals end4 ,supposing then we wish to send the following message3 ,send #f1jjj cavalry at once1 and that the key word was ,washington4 ,following the instructions heretofore given for enciphering1 we would place the words as follows3 ,,washingtonwashingtonwashi ,,sendxx#fjjj,,xxcavalryatonce ,,ewfelqbkfezdqhnnycqndmffe ,in place of a disk means may be extemporized by taking two strips of paper1 on one of which the alphabet1 numerals1 etc41 are twice written in succession4 ,on the other1 with equal spacing1 the alphabet1 etc41 are written once1 but in reverse order4 ,by sliding these strips in juxtaposition with each other they will replace the disk4 ,cipher disks should never be allowed to fall into the hands of the enemy or of anyone unauthorized to have and use them2 to insure this1 special instructions should be issued for their care and keeping4 ,,the ,,mathematical ,,cipher4 ,this cipher is a highly efficient one for the purpose of secrecy and at the same time requires no apparatus whatever attendant upon its use4 ,the cipher is constructed as follows3 ,commit to memory the alphabet by numbers1 viz1 ,a1 #a2 ,b1 #b2 etc4 ,take any key word1 phrase1 or sentence desired2 for example1 ,a discovery4 ,suppose the message to be enciphered is ,send me powder tonight4 ,the enciphering of the message using the key given above will be as follows3 ,to encipher1 first write out the key1 letter by letter1 placing the message letter by letter beneath it4 ,then reduce the letters of the key and the message to the numeral alphabetical equivalents4 ,add the individual columns and subtract unity from each4 ,from any result thus found1 which exceeds the number of letters in the alphabet1 the number #bf must be subtracted4 ,the final totals reduced to letters by numerical alphabetical equivalents will then give the cipher4 ,,adiscoveryadiscover sendmepowdertonight which reduced to numerical equivalents according to alphabetical position of letters becomes3 #a #d #i #ai #c #ae #bb #e #ah #be #a #d #i #ai #c #ae #bb #e #ah #ai #e #ad #d #ac #e #af #ae #bc #d #e #ah #bj #ae #ad #i #g #h #bj ,now add the columns and subtract unity from each4 ,if any result so found exceeds the number of letters in the alphabet #bf must be subtracted from it4 ,in the example given the numerical totals are as follows3 #bj #i #bc #bc #af #bj #ch #bj #da #bi #f #bb #bi #cd #ag #bd #bi #ac #ch #a #a #a #a #a #a #a #a #a #a #a #a #a #a #a #a #a #a #a ---------------------------------------- --------------- #ai #h #bb #bb #ae #ai #cg #ai #dj #bh #e #ba #bh #cc #af #bc #bh #ab #cg #bf #bf #bf #bf #bf #bf #bf ---------------------------------------- --------------- #ai #h #bb #bb #ae #ai #aa #ai #ad #b #e #ba #b #g #af #bc #b #ab #aa which connected to letters gives3 ,,shvvosksnbeubgowblk the cipher required4 ,translation of cipher is had by reversing the processes described4 ,,the ,,route ,,cipher4 ,this is a cipher in which the words or a message are retained unchanged1 but are so disarranged by preconcerted rules that the sense becomes unintelligible4 ,the message as received seems to be a number of disconnected words and without meaning1 but by arrangement in proper order in accordance with certain rules can be easily read4 ,messages enciphered in this manner may be translated by persons not in possession of the key1 and therefore the information contained therein should only be of such a character as to be of little value to the enemy unless acted upon immediately4 ,the usual method employed in arranging a message for this cipher is to write the words in vertical columns4 ,the number of words in each column should always equal the number of columns1 being made so1 if necessary1 by the addition of sufficient blind words4 ,a preconcerted route is agreed upon1 as up to the first column1 down the third1 up the second1 etc4 ,the message is then transmitted without reference to the columns1 but is deciphered at the receiving station by column arrangement and perusal along the original route4 ,for example1 to encipher the message ,move daylight4 ,enemy approaching from north4 ,prisoners say strength one hundred thousand4 ,meet him as planned1 arrange as follows3 ,move strength planned say daylight one as prisoners enemy hundred him north approaching thousand meet from ,here the route is down the first column1 up the fourth1 down the second1 and up the third4 ,,cipher ,,detection4 ,general instructions4--,in deciphering a message in which the same cipher letter or symbol is uniformly used to represent the same text letter1 the following data will be of assistance4 ,the proportion of occurrence of letters of the alphabet in ,english words is as follows3 ,for every #b of the letter ,q there are #d of the letter ,x1 #h of ,k1 #af of ,b1 #ac of ,c1 #hj of ,i1 ,n1 ,o1 and ,s2 #he of ,a1 #ij of ,t1 and #abj of letter ,e4 ,the compounds most frequently met with are ,,ng ,,ee ,,ll ,,mm ,,tt ,,dd and ,,nn4 ,the order of frequency in which the letters of the alphabet occur as initial letters in words is as follows3 ,s1 ,c1 ,p1 ,a1 ,d1 ,i1 ,f1 ,b1 ,l1 ,t4 ,employment of ,cipher ,disk4 ,if messages are enciphered by a mere transposition of the letters of the alphabet1 the cipher disk can be used to quickly decipher the message1 as the following example will show3 ,assuming that ,f is used to represent ,a1 ,g to represent ,b1 ,h to represent ,c1 ,i to represent ,d1 ,j to represent ,e1 etc41 in regular sequence1 and that the message to be enciphered is3 ,we are short of rifle ammunition2 send #cj1jjj rounds at once4 ,this would be enciphered if divided into groups of four letters as follows3 jbfo bnyr omra oxub fuls xmxr snbs cmjb smhm yrln fsco rlsc nfmr sdb4 ,place a of the upper cipher disk under ,b of the lower disk and notice whether the cipher letters jbfo--the first group--are intelligible4 ,they give sawn1 continue this for saw1 the first three letters1 may be the text word4 ,now the next group is ,b ,n ,y ,r and these give ,a ,o ,d ,k4 ,we know that ,a does not represent ,b because the first #h cipher letters give the meaningless letters sawnaodk4 ,turn a to ,c and we have for the first group ,t ,b ,x ,o1 which is without meaning4 ,turning a to ,d we get ,u ,c ,y ,p1 a meaningless jumble4 ,turn a to ,e and we get ,v ,d ,z ,q1 which is meaningless4 ,now turn a under ,f and we find that ,,jbfo mean ,wear1 which1 so far at least1 gives us a part of a word1 or the word ,we and part of another word4 ,we continue to the next group ,b ,n ,y ,r1 which gives us esho4 ,we now have these letters ,wearesho1 which at a glance we read ,we are sho2 continuing to the next group ,o ,m ,r ,a the cipher disk gives us rtof1 and we read ,we are short of and know we have found the key letter1 and the information hidden in the cipher is ours4 ,continue deciphering with a under ,f until the end of the message4 ,sometimes the key letter is changed after two1 three1 or four letters4 ,it is a matter of minutes only to run through the alphabet and learn the meaning of a message so enciphered4 ,,chapter ,,vii4 ,,field ,,glasses ,,and ,,telescopes4 ,reflection--refraction--lenses4 ,illustration3 ,,fig4 #bj4 ,when light falls on a transparent body1 part is reflected and part is refracted4 ,the angle which the ray makes with the normal1 or perpendicular1 to the surface at the point of contact is known as the angle of incidence1 and the angles which the reflected and refracted rays make with the same normal are known respectively as the angle of reflection and refraction4 ,the reflected ray makes the same angle with the normal as the incident ray1 while the refracted ray1 when passing from a rarer to a denser medium1 is bent toward the normal1 and vice versa2 the denser the medium into which the ray passes the greater is the deviation4 ,this law allows us at once to understand the action of a lens1 which may be defined as a transparent medium that from the curvature of its surface causes the rays of light traversing it to either converge or diverge4 ,the ordinary lenses have either spherical surfaces or a combination of spherical and plane surfaces4 ,this combination will give rise to six classes 7fig4 #bj73 7a7 ,double convex2 7b7 plano convex2 7c7 double concave2 7d7 plano concave2 7e7 converging1 and 7f7 diverging meniscus4 ,those lenses which are thicker at the center than at the edges are converging or concentrating lenses1 and those which are thicker at the edges than the center are diverging4 ,,focus--,,optical ,,center4 ,the focus of a lens is the point where the refracted rays or their prolongation meet2 if the rays themselves intersect after refraction the focus is real1 and if their prolongations meet the focus is virtual4 ,the line passing through the centers of curvature of the two surfaces of a lens is called the principal axis and contains a point known as the optical center1 which has the property by virtue of which1 if a ray passes through it1 the ray will not be deviated4 ,the optical center can always be found by drawing two radii parallel to each other1 one from each center of the curvature of the surface until the radii intersect their respective surfaces1 then draw a line joining these two points4 ,the intersection of this last line with the principal axis will give the optical center4 ,,image--,,conjugate ,,foci4 ,let ,,ab be the section of a double convex lens and ,c and ,d 7fig4 #ba7 be the centers of curvature of the two surfaces4 ,draw the lines ,,cd and ,,de from ,c and ,d parallel to each other1 then join ,d and ,e by a straight line4 ,the point ,o will be the optical center of the lens4 ,let us take a point ,r1 on the principal axis as a source of light2 the ray ,,rd passes through the optical center and is not deviated4 ,the ray ,,rk on striking will be refracted in the direction ,,kg toward the perpendicular to the surface ,,kd in accordance with the law of refraction1 as glass is denser than air4 ,on emerging at ,g it is refracted away from the perpendicular to the surface ,,cg1 since it passes from a denser to a rarer medium1 and will intersect the ray ,,rd at the point ,r4 ,in a like way the ray ,,rk will be found to intersect the ray ,,rd at the same point1 ,r1 which is the focus for all rays coming from ,r4 ,the point ,r is said to be the image of the object ,r1 and when the two points are considered together they are called conjugate foci4 ,if the incident beam is composed of parallel homogeneous light1 the rays will all be brought to a focus at a point on the principal axis1 called the principal focus of the lens1 and the distance of this point from the optical center is the principal focal length1 which is always a fixed quantity for any given lens4 ,illustration3 ,,fig4 #ba4 ,,law ,,of ,,foci4 ,there is a fixed relation between the principal focal length of a double convex lens and the position of the image of the object which may be expressed as follows3 #a_/;i #a_/;f - #a_/o1 in which i and o are the distances of the image and object1 respectively1 from the optical center and f the focal length1 from which we see that for all positions of the object from an infinite distance away from the lens to double the principal focal distance1 the image will be on the other side1 between a distance equal to the principal focal length and double this length4 ,these are the limits of the image and object in the ordinary cases4 ,if we place this expression in the following form3 i of_/7o - f71 and suppose the object to remain the same distance from various lenses1 it will be seen that the image will be closer to the lens which has the shorter focal length4 ,the principal focal distance1 or1 briefly1 the focal length of the lens1 depends on the curvature of the surfaces1 and the greater the curvature the shorter the focal length4 ,,formation ,,of ,,image4 ,illustration3 ,,fig4 #bb4 ,let us now see how an image is formed by a convex lens1 and suppose that ,,cd is the section of a double convex lens 7fig4 #bb71 ,o the optical center1 and ,,ab an object at a greater distance from the optical center than double the focal length4 ,rays will pass out in all directions from the object and some will fall on the lens4 ,a ray from ,a will pass through the optical center and will not be deviated2 others will be incident at various points1 for example1 ,e and ,g1 and if we apply the law of refraction we will find that ,,ae and ,,ag will intersect each other and ,,ao at the point ,a1 provided we do not consider the figure of the lens1 forming one point of the image ,a ,b2 similarly for rays from other points of the object1 as1 for example1 ,b1 we can construct the focus ,b1 and thus obtain the image ,a ,b1 which is inverted and smaller than the object ,,ab4 ,the relative size of the image and object will be directly as the conjugate foci1 and these can be found at once from the equation of the lens4 ,,spherical ,,aberration4 ,if1 however1 we consider the form of the lens1 we will find that all the rays emerging from one point on the object are not brought to the same focus1 because the rays incident on the edges of the lens are refracted to a greater extent than those falling on the center1 and will be brought to a focus at a shorter distance from the lens than those passing through the central part4 ,this confusion or wandering of the foci from one point is called spherical aberration1 or aberration of form1 and is due solely to the geometrical form of the lens4 ,,chromatic ,,aberration4 ,in what has been said about the visual image we have supposed that the light was monochromatic1 or homogeneous4 ,let us see what will happen if the light is polychromatic1 say1 for example1 sunlight1 and let a beam of sunlight be intercepted on a screen after passing through a double convex lens4 ,it will be observed1 as in figure #bc1 that the violet rays are brought to a focus nearest the lens1 and the red farthest away1 and circles of light will be seen on the screen2 this wandering of the colored rays from a common focus is called chromatic aberration and depends on the dispersive properties of the material of which the lens is made4 ,here is a defect that can not be corrected by a stop1 but as the refractive and dispersive properties of a substance do not vary together1 it is possible to combine two substances1 one with high refractive and low dispersive properties and the other with the reverse properties4 ,if proper curves are given to them they will correct each other1 thereby producing coincidence of the visible and chromatic foci4 ,such a combination gives an achromatic lens1 which is usually composed of a double convex of crown glass cemented to a diverging meniscus of flint glass1 as shown in section in figure #bd4 ,this combination is not absolutely achromatic1 but sufficiently so for all general purposes4 ,illustration3 ,,fig4 #bc4 ,illustration3 ,,fig4 #bd4 ,,telescopes4 ,the telescope is an optical instrument based on an object glass or reflector to form a real image of a real and distant object1 and of an ocular to magnify and view the image4 ,telescopes are classified as refracting or reflecting according as the object glass is a lens or a reflector4 ,the object glass must be essentially convex if the telescope is a refractor1 and if a reflector1 the object mirror must be concave2 the ocular may be either concave or convex4 ,there are four types of refractive telescopes used for military purposes1 viz3 #a4 ,the astronomical4 #b4 ,the terrestrial4 #c4 ,the galilean4 #d4 ,the prismatic4 ,figure #bf is a section of an astronomical telescope4 ,the object glass 7,d7 is a combination consisting of a double convex and a double concave lens cemented together with ,canada balsam4 ,the double concave lens is added to correct for chromatic aberration4 ,the ocular 7,e7 is a convex-concave lens4 ,rays of light from some distant object are converged by the objective 7,d7 and form an inverted image 7ab7 at the focal plane 7,f74 ,the eye lens 7,e7 receives the divergent pencils from a and b and bend them so that they enter the eye as if coming apparently from the direction of a b where the apparent image is seen4 ,from the eyepiece 7,e7 the rays emerge in a cone of pencils of light smaller than the pupil of the eye1 which enables a telescope of this type to have a large field of view4 ,the image1 however1 is inverted and the astronomical telescope in its original form is therefore not suitable for military purposes4 ,in a modified form it is much used1 as will be shown in a later paragraph4 ,illustration3 ,figure #bf ,figure #bg is a section of a terrestrial telescope much used for military purposes4 ,glasses of this type are quite generally known as spyglasses4 ,as in the case of the astronomical telescope1 the first inverted image ba is formed at the focal plane 7,f71 and the first eyeglass converges these pencils to ,l4 ,instead of placing the eye at ,l1 as in the astronomical telescope1 the pencils are allowed to cross and fall on a second eyeglass1 by which the rays of each pencil are converged to a point in the second erect image a b1 which image is viewed by means of the third and last eyeglass4 ,illustration3 ,figure #bg ,terrestrial telescopes have a comparatively small field of view4 ,the barrels of this telescope are necessarily long on account of the additional lenses4 ,,galilean ,,field ,,glasses ,,and ,,telescopes4 ,figure #bh is a section of a ,galilean telescope which differs from the astronomical telescope in having a double concave instead of a double convex1 eyepiece or ocular4 ,in this telescope the rays from an object are converged by the object glass 7,o7 and would normally focus at the focal plane 7,c7 and there form the inverted image ba were it not that the double concave eyeglass or ocular 7,d7 is so located in the barrel of the telescope as to intercept the pencils before they are focused4 ,this double concave eyeglass diverges these pencils and forms a magnified erect image a b apparently at ,e4 ,due to the diverging action of this concave eye lens1 the cone of pencils entering the eye is larger than the pupil of the eye1 and therefore but a small part of the field gathered by the object glass is utilized by the eye1 which causes telescopes of this type to have a comparatively small field of view4 ,illustration3 ,figure #bh ,,porro ,,prism ,,field ,,glasses ,,and ,,telescopes4 ,in #ahej a ,french engineer1 ,porro1 discovered a combination of prisms which1 when inserted between the objective and the eyepiece of an astronomical telescope1 showed the image erect or in its natural position1 while the same telescope without the prisms showed the image inverted4 ,practical use of this discovery was not made for many years after4 ,these prisms served a twofold purpose1 viz1 showing the image of the object looked at in its natural position instead of reversed1 and second1 the shortening of the telescope by twice turning the ray of light upon itself4 ,each tube of the prism field glass contains two of these double-reflecting prisms4 ,the ray of light passing through the object glass enters the first prism in such a manner as to be twice totally reflected1 each time at an angle of #ij1 thus emerging parallel to the entering ray1 but in the opposite direction4 ,it is thus caught by the second prism and is similarly reflected and sent on its original direction without change except in one very important point1 viz1 the image of the object observed1 which1 without the intervention of the prism1 would be upside down1 is now erect1 and will be magnified by the simple astronomical eyepiece just as the stars and planets are magnified in large telescopes4 ,the field of view of the ,porro prism glass is considerably larger than that of the ordinary field glass4 ,it decreases about #ab per cent with each magnifying power1 a number #f-power glass giving a linear view of #aah feet in a thousand1 while in a number #aj glass the field is but #gj linear feet4 ,this is explained as follows3 ,the rays of light emerging from the ocular of the ,galilean telescope are divergent and cover an area much greater than the size of the pupil of the eye4 ,as all rays falling outside the pupil of the eye are lost1 but a small field of view can be seen1 as in looking through an ordinary cone from the larger end4 ,the prism glasses are constructed on the opposite principle4 ,the rays of light gathered by the objective emerge from the eyepiece in a converging pencil of light small enough to enter the pupil of the eye1 thus giving a larger field of view2 theoretically1 nine times the area given by the old-style instrument of the same power4 ,with these advantages1 however1 the ,porro prism glass has not been found in all respects satisfactory for field service4 ,with a clear atmosphere and the object which is being viewed well illuminated1 it is distinctly superior to the ,galilean field-type glass in respect to light1 power1 and definition4 ,the prisms having once been deranged1 however slightly1 satisfactory use of the glass can not be had until the prisms have been readjusted1 and until very recently it was impracticable to have this done elsewhere than at the place of manufacture of the glass4 ,illustration3 ,,fig4 #bi4--,porro prism4 ,,field ,,glasses4 ,the field glass or binocular is a combination of two similar telescopes and possesses mechanical adjustments capable of focusing the two telescopes simultaneously or separately1 depending upon the type considered4 ,field glasses are divided into two general classes1 viz1 the ,galilean glasses and the ,porro prism glasses4 ,,properties ,,of ,,telescopes ,,and ,,field ,,glasses4 ,telescopes and field glasses have four properties1 viz1 power1 light1 field1 and definition4 ,these properties are expressed in terms of the corresponding qualities of the unaided eye4 ,eyes are of very different capabilities4 ,some people have short sight while others have far sight4 ,there are normal1 excellent1 and weak eyes4 ,in the following discussion the capabilities of the normal eye are assumed4 ,for each individual there is a certain distance at which objects may be most distinctly seen4 ,this is called the visual distance4 ,with shortsighted eyes this distance is from #c to #f inches2 with normal eyes1 from #h to #ad inches1 and with farsighted eyes1 from #af to #bh inches4 ,the capabilities of the normal unassisted eye may therefore be expressed as follows3 ,power1 #a2 light1 #a2 field1 #de2 definition1 #dj to #c4 ,power4--,at the visual distance1 all objects seen by the unaided normal eye appear in their natural size4 ,at less than the visual distance they appear indistinct1 blurred1 and imperfectly defined2 at greater than the visual distance objects are clear and well defined1 but diminish in size1 the more so as they are farther removed4 ,the ability of a lens to magnify the apparent diameter of an object is termed its power4 ,the power of a lens is defined as the ratio of the diameter of the object as seen through the lens to the diameter as viewed by the unaided eye4 ,the power is also defined as the ratio of the focal distance of the object glass to that of the eyepiece4 ,the power of a field glass can be roughly determined by focusing the instrument on a wall or a range rod1 by looking at the object through the instrument with one eye and at the same object directly with the unaided eye4 ,a comparison of the diameter of the two images gives the ratio4 ,the power of a telescope or a field glass can more accurately be measured by means of a dynameter1 which is a microscope which can be fitted over the eyepiece end of the instrument1 and which magnifies the image4 ,the end of the dynameter next to the eyepiece of the instrument is ruled with a series of lines one-hundredth of an inch apart4 ,on focusing the dynameter1 the image of the emerging pencil appears as a sharply defined ring of light with the magnified scale of the dynameter across it4 ,the number of subdivisions covered by the diameter of the ring of light is noted4 ,the diameter of the object glass is similarly measured by means of a pair of dividers and read to the hundredth part of an inch4 ,the ratio of the diameter of the object glass to that of the image as seen in the dynameter gives the power of the instrument4 ,this method is not applicable in the case of the ,galilean telescope or the field glass consisting of two ,galilean telescopes1 due to the fact that the rays from the eyepiece of the ,galilean telescope are divergent4 ,field glasses in which the image appears magnified from one to six diameters are known as low-power glasses4 ,field glasses which produce an image magnified over six diameters are termed high power4 ,for the mounted man a glass of but #d1 or at most #f1 powers1 can be used with advantage2 on foot1 with free hand1 instruments of not to exceed #aj powers can be used4 ,if more than #aj powers are desired1 a holder becomes necessary1 and if the holder is intended to be portable a greater power than #ej is not practicable1 as the movement of the air or the slightest touch of the hand sets up vibrations that render clear vision impossible4 ,field glasses with low magnifying power1 which are usually preferred by ordinary observers1 have their chief value in the comparatively extensive field of view2 they should be used to observe extensive movements1 where large tracts of country must be taken in one field of view or in sweeping the landscape to find the tents of the enemy1 their wagons1 etc41 or other objects1 to be afterwards more closely examined with the telescope4 ,they may be used on shipboard or in boats1 where the rolling motion interferes with the use of the telescope2 also on horseback or in hasty examination made on foot or in trees1 and generally for all observations not critical or those to be made under circumstances where the telescope can not be conveniently handled4 ,the field glass ought to be held by both hands when in use1 and to steady it the arms should be kept close to the body4 ,for reading signals at short ranges1 say1 up to #e miles1 these glasses are better than the telescope4 ,flag signals have frequently been read with glasses of this description at a distance of #aj miles4 ,light4--,the illumination of an object when observed with the unaided eye is impressed upon the retina with a brightness in strict proportion to that of the object itself4 ,if an object be viewed under equal illuminating conditions alternately with the naked eye and with a glass1 the brightness of the image seen with the naked eye may be represented by #a1 while that of the image in the glass will generally differ1 being greater or less4 ,the light of the telescope or field glass is expressed by the number which shows how many times brighter the object appears through the instrument than to the naked eye4 ,light is a function of the dimensions of the object glass and of the power of the instrument1 and is sometimes determined by dividing the square of the objective aperture 7expressed in millimeters7 by the square of the power4 ,the light of a telescope or field glass can also be determined by means of the absorption apparatus shown in figure #cj 7a7 7b7 7c74 ,this absorption apparatus operates on the principle of viewing an object through a perfectly black liquid1 which absorbs all colors equally1 and of increasing the thickness of the liquid layer until the object becomes invisible4 ,the thickness of the layer of liquid will then be a measure of the relative brightness or intensity of the illumination4 ,illustration3 ,,fig4 #cj7;a7 ,,fig4 #cj7;b7 ,,fig4 #cj7;c7 ,the apparatus consists of two wedge-shaped vessels1 made of brass1 with glass windows in the sides4 ,one of these vessels is shown in perspective in figure #cj;a4 ,the sides ,a and the one opposite are of glass4 ,b is tubulure for filling the apparatus1 and is stopped with a cap4 ,the operation of the apparatus is shown diagrammatically in figures #cj;b and #cj;c4 ,the edges of the two wedges which come together are divided into scales of equal parts of convenient magnitude4 ,each scale begins with zero2 not at the extreme point of the wedge outside1 but at a point1 which1 allowing for the thickness of the glass sides1 is opposite the point of the wedge of liquid inside4 ,it will be observed in figures #cj;b and #cj;c that the sum of any two adjacent numbers1 on the respective scales1 over the whole overlapping portion of the wedges1 is the same4 ,thus in figure #cj;b it is #aa1 and in figure #cj;c it is #g4 ,these figures measure the relative thickness of the liquid layers in the two respective settings of the apparatus4 ,suppose the image is just obliterated1 when looking with the unaided eye1 at the setting shown in figure #cj;b1 and when using the glass at the setting shown in figure #cj;c4 ,this would mean that the illuminating power of the glass is seven-elevenths4 ,in using the apparatus1 a focusing cloth1 used by all photographers1 is useful in excluding stray light4 ,field4--,maintaining the head and eyes as motionless as possible1 the field of vision of the unaided eye or the range within which objects can be perceived by the unaided eye varies according to direction4 ,de ,schweinitz gives the following limits3 ,outward1 #ij2 outward and upward1 #gj2 upward1 #ej2 upward and inward1 #ee2 inward1 #fj2 inward and downward1 #ee2 downward1 #gb2 downward and outward1 #he4 ,it may be safely said that the field or visual angle of the unaided eye for distinct vision is at least #de in all directions4 ,the visual angle or field of a field glass is always smaller1 no field glass having yet been designed which could equal the field of the unaided eye4 ,the field of a telescope or field glass can best be determined by the use of a transit or other instrument used in measuring horizontal angles4 ,the glass is placed upon the telescope of the transit in such a way that the axes of collimation of the transit and the telescope or field glass are parallel4 ,the extreme limits of the field of view are marked and the horizontal angle between the markers noted on the limb of the transit4 ,definition4--,one of the chief qualities of the eye is its power of defining outlines and details distinctly4 ,relative characteristics in this respect may be determined in various ways4 ,thus the distance at which printed matter can be read1 or the details of a distant object distinguished1 will give a fair measure of the defining power of the eye2 but a better method is to express the definition of sight by angular measurement--that is1 by the determination of the smallest visual angle giving clear results4 ,experience teaches that this angle of the normal eye 7with good light and favorable color conditions7 is about #dj1 and it is therefore possible to determine the smallest object which can just be seen1 well defined1 at an arbitrary distance4 ,for instance1 at a distance of #ae feet an object can be seen which is one-twentieth of an inch high or broad2 at #cj feet distance1 consequently1 the object must be twice the size 7one-tenth of an inch7 to be seen1 and so on relatively1 within limits1 as distance increases4 ,but as the distance becomes greater sharpness of vision is impaired materially by the interposing atmosphere1 while it is also affected by color contrasts and conditions of illumination4 ,it therefore follows that at considerable distances objects which subtend a visual angle of #dj are no longer clearly defined but become so only as the angle approaches #fj1 #abj1 #ahj1 or more4 ,the most important and essential quality of a telescope or field glass is definition1 i4 e41 the sharpness1 clearness1 and the purity of the images seen through it4 ,to obtain good definition it is necessary that spherical and chromatic aberration be overcome1 that the polish of the lenses be as perfect as possible1 that the cement possess no inequalities1 and that the lenses be well focused1 that there be no dampness in the interior of the tubes1 and1 generally1 that the instrument be without optical defect4 ,faults in this direction are discovered at once by examination of definition1 whereas in determining the other constants they are less noticeable4 ,in comparing the definition of any two instruments it is ordinarily necessary only to scan distant objects and observe to what extent details may be distinguished4 ,the following test may also be used3 ,focus on printed matter at a distance just beyond that at which perfect clearness is given and gradually approach until the letters are distinctly defined4 ,the instrument with which the print can be read at the greatest distance has the best definition4 ,to express definition as an absolute measure1 use instead of printed matter1 a white sheet of paper upon which a series of heavy lines are drawn at intervals equivalent to their thickness4 ,focus upon this and gradually approach from a point where the impression of a uniform gray field ceases and the black lines and white intervals begin to appear distinct and defined4 ,let the distance thus found be #bj yards and the thickness of the lines and intervals between them one-tenth inch4 ,the circumference of a circle with a radius of #bj yards or #g1bjj tenths inches is #ad1djj by #c4adaf or #de1bdj tenth inches2 but a circumference equals #cfj or 7#cfj by #fj by #fj7 #a1bif1jjj4 ,if1 therefore1 #de1bdj tenths inches correspond to #a1bif1jjj1 then #a tenth inch equals #a1bif1jjj divided by #de1bdj1 or #bh4f4 ,the definition is therefore #bh4f1 or practically half a minute4 ,the capabilities of glasses1 including telescopes1 in a general way1 lie between the following limits3 7#a7 ,power between #b and #a1jjj4 7#b7 ,light may be #j4ja to #bjj times that of the unaided eye4 7#c7 ,field measures in most favorable case1 #aj2 in the most unfavorable1 4#ja4 7#d7 ,definition varies between #dj and #j4a4 ,thus1 as a maximum1 an object may be seen by means of a telescope1 magnified #a1jjj times1 #bjj times brighter and #djj times sharper than with the naked eye4 ,if these advantages could be fully utilized for military purposes the use of glasses would be extraordinary1 a power of #a1jjj practically effecting the same purpose as the approach of the observed object to one-thousandth of the distance4 ,a hostile command #aj miles distant could be seen theoretically as well as if they were only #ec feet away1 and the slightest movement of each single man would become visible4 ,of course no such wonderful effect is physically practicable1 and the limiting conditions increase greatly in proportion as either one or the other of the qualities1 power1 field1 etc41 is especially sought4 ,while astronomers require only that the telescope be made as capable and perfect as possible in an optical point of view1 making all other conditions subordinate to this one1 the military1 to whom the glass is simply an accessory1 make other conditions of the first importance4 ,the glass must have suitable form1 small volume1 little weight1 and that it may be used without support1 mounted or dismounted1 and the image must appear as looked at by the naked eye--that is1 not inverted4 ,the capability of the instrument1 however1 is thereby much limited2 great powers give plain images only with relatively long tubes2 glasses must be held the steadier the more they magnify2 and with increasing power all vibrations become more troublesome and render minute observations very difficult or impossible4 ,the additional lenses in terrestrial telescopes somewhat decrease power and affect also light and definition4 ,it is clear therefore that expectations of achieving great power should not be entertained1 the function of field glasses being to bring out and define objects which to the naked eye appear indistinct and doubtful4 ,the distinctness with which anything can be seen through the telescope depends1 primarily1 upon the number of straight lines of light which are collected by it from every point of the object4 ,telescopes1 the object glasses being equal in size1 diminish light as a general rule in proportion as their magnifying power is great4 ,the most powerful glasses are therefore to be used for minute observations on the clearest days or when there is a strong light upon the observed object4 ,when the light is fading or there is a little light upon the observed object the clearer view will be had with glasses of large field and low magnifying power4 ,,field ,,glasses ,,and ,,telescopes ,,issued ,,by ,,the ,,signal ,,corps4 ,the ,signal ,corps issues four standard field glasses1 viz1 ,type ,a1 ,type ,b1 ,type ,c1 ,type ,d4 ,field glasses issued by the ,signal ,corps are not supplied for the personal use of an officer and will not be used in lieu of the officer's personal field glass prescribed by paragraph #ig1 ,general ,orders1 #afi1 ,war ,department1 #aijg 7,par4 #a1 ,g4 ,o4 #af1 ,war ,dept41 #aiaj74 ,under paragraph #aehb1 ,army ,regulations1 as amended by paragraph ,i1 ,general ,orders1 ,no4 #bjg1 ,war ,department1 ,october #af1 #aiji1 the ,signal ,corps will sell field glasses to officers of the army for their personal use4 ,application for the purchase of field glasses should be addressed to the ,chief ,signal ,officer of the ,army1 ,washington1 ,d4 ,c41 inclosing post-office money order or check on the ,treasurer or ,assistant ,treasurer of the ,united ,states for the amount1 payable to the ,disbursing ,officer1 ,signal ,corps1 and ,signal ,corps ,form ,no4 #bdj accomplished in duplicate4 ,the ,government does not pay transportation charges for the shipment of articles sold to officers4 ,field glasses are sent from the ,signal ,corps ,general ,supply ,depot1 ,fort ,wood1 ,new ,york ,harbor1 by express1 charges collect1 unless purchase request is accompanied by funds so that field glasses may be sent by registered mail4 ,forwarding by registered mail is somewhat cheaper than by express1 and the amount of postage required is #dj cents for ,type ,d glass1 #df cents for ,types ,a and ,b1 and #gd cents for ,type ,c4 ,express charges depend upon the distance from ,new ,york4 ,the ,signal ,corps has purchased many samples of field glasses from various manufacturers with a view of testing their suitability for the military service4 ,these samples may be examined by officers of the army at the signal office in ,washington4 ,among these samples there are many excellent glasses especially suitable for the military service1 but the higher grades are too expensive for general issue to line organizations in large quantities4 ,officers desiring an especially fine field glass should inspect the samples referred to2 these1 however1 are not for sale by the ,government1 but information will be supplied concerning dealers and cost4 ,no advice or fixed rule can be stated as to what constitutes the most suitable characteristics of a field glass4 ,no single field glass can furnish maximum results under all conditions on account of varying conditions of the atmosphere4 ,a high-power glass is unsuitable for use at night1 hazy atmosphere1 or for use of a mounted man where the glass can not be rested against a firm support4 ,a low-power glass with large object lens to permit as much light as possible is a necessary condition for use at night4 ,the double power glass which is issued as a part of the visual signaling outfits was designed for the military service as a compromise for conflicting conditions4 ,a brief description of the field glasses issued by the ,signal ,corps1 together with the cost of the same1 is given below4 ,type ,a3 ,this glass is the current result of the efforts of the ,signal ,corps to provide a field glass that will meet the greatest variety of conditions1 and insure efficient service to the greatest number of military observers4 ,it is really two glasses in one--a day glass of medium power1 and a night glass of low power4 ,illustration3 ,,fig4 #ca4--,type ,a4 ,showing the field glass and case with sling cord1 shoulder straps1 belt loops1 and compass4 ,it is to be clearly understood that while this glass is considered superior for moderate ranges1 it does not replace1 under special conditions1 for long ranges1 either the porro prism glass or the telescope4 ,when held as shown in figure #cb with the tubes drawn out about #a inch to secure proper focus1 the glass has a power of about #e4f diameters1 and a field of about #e4d degrees4 ,illustration3 ,,fig4 #cb--,signal ,corps field glass1 ,type ,a4 ,if the glass is turned into the position shown in figure #cc1 the small plus lenses1 just in front of the eye pieces1 drop automatically into position and reduce the power to #c4h diameters1 and increase the field to #h4c degrees4 ,this position requires a different adjustment1 the tubes being drawn out about one-third of an inch to get the proper focus4 ,it will be observed in the illustrations that the rear bar of the frame is not only lettered to indicate which power is being used1 but the bar itself is shaped with a hump on one side1 and hollowed on the other4 ,when the hump is up1 the low power is in use4 ,this is to facilitate adjustment in the dark4 ,the action of the small automatic lenses is free and positive4 ,neither the eyepieces nor the sections containing the small lenses should be unscrewed1 except in case of necessity1 and then not by unskilled hands4 ,illustration3 ,,fig4 #cc4--,signal ,corps field glass1 ,type ,a4 ,the frame1 of aluminum and brass1 is composite1 to give lightness and strength2 and while it is constructed to withstand the rough handling of field service1 no field glass is proof against careless or wanton treatment4 ,the tubes are covered with tan leather1 and a round sling cord1 braided from four strands of pliable tan leather1 is fastened by snaps to eyes in the frame4 ,the case is of tan calfskin1 provided with shoulder strap1 and has an efficient small compass set into the cover4 ,two loops are sewed to the back of the case so that it may be worn on a belt4 ,the glass1 complete with case1 cord1 and straps1 weighs #ba4e ounces4 ,two of these glasses are issued to each company of infantry and coast artillery1 ,philippine ,scouts1 and ,signal ,corps1 and to each troop of cavalry for use in instruction in visual signaling4 ,below is a brief description of the type ,a glass4 ,magnification1 #c and #e diameters2 ,galilean type2 object lens1 #a inches2 tan leather finish2 tan leather carrying case with compass2 weight of glass1 complete1 with case1 cord1 and strap1 #be ounces4 ,at a distance of #a1jjj yards the field of view includes a diameter of #abc yards for the #c power1 and #gc yards for the #e power4 ,length of glass closed1 #d inches4 ,this glass is issued as a part of the visual signaling kit to each company of infantry1 coast artillery1 and ,philippine ,scouts1 troop of cavalry1 machine-gun platoon1 and ,signal ,corps field company4 ,price1 #ab4ae4 ,the latest issue of this glass known as the ,type ,a1 model #aiaj1 includes provision for interpupillary adjustment1 the two barrels being hinged to accommodate the glass to the distance between the pupils of the eye4 ,the price of the model #aiaj glass is #ad4ge4 ,type ,b3 ,this field glass is similar in appearance and construction to the ,type ,a glass1 and is issued to the field artillery organizations upon requisition4 ,the following is a brief description3 ,magnification1 #d and #f diameters2 ,galilean type2 object lens1 #a inches2 interpupillary adjustment2 tan leather finish2 tan leather carrying case with compass2 weight of glass1 complete1 with case1 cord1 and straps1 #bf ounces2 length of glass closed1 #d inches4 ,at a distance of #a1jjj yards the field of view includes a diameter of #ij yards for the #d power1 and #fj yards for the #f power4 ,this glass is issued as a part of the fire-control equipment to field artillery4 ,price1 #ag4ej4 ,type ,c3 ,the type ,c is a high power glass of the porro prism type and is issued only to certain organizations of the field artillery1 ,signal ,corps1 and to all machine-gun platoons4 ,description4--,magnification1 #aj diameters2 prismatic type2 object lens1 #a inches2 interpupillary adjustment2 tan leather finish2 sunshade2 tan leather carrying case2 weight of glass1 complete1 with case1 cord1 and straps1 #df ounces2 length of glass closed1 #g inches4 ,at a distance of #a1jjj yards the field of view includes a diameter of #hj yards4 ,this glass is issued to reconnaissance officers of field artillery4 ,price1 #ci4ij4 ,type ,d3 ,purchase has been made for delivery in the near future of a supply of a new type of high power prismatic field glass for sale and issue4 ,this new type of glass1 to be known as type ,d1 is considerably smaller than the type ,c glass1 as is shown by figure #cd4 ,the glass in a tan-colored carrying case weighs #ae ounces1 the field glass without the case weighing but #i ounces4 ,the magnification is #h powers and the field of view 7with both eyes7 #e #dj4 ,the estimated cost will be #bg4 ,,telescopes ,,issued ,,by ,,the ,,signal ,,corps4 ,type ,a3 ,this glass complete consists of a #b-;inch prism terrestrial telescope1 powers #ah and #bd1 with alt-azimuth1 folding tripod1 and carrying case4 ,type ,b3 ,this telescope is a #ai-bg power1 #b-;draw terrestrial telescope1 in leather carrying case with sling4 ,the leather carrying case also includes a holder which can be screwed into a tree1 post1 or other stationary wooden object4 ,,general ,,specification ,,no4 #bfc4 ,revised ,february #aj1 #aiaj4 ,,service ,,field ,,glasses4 #a4 ,preliminary4--,this specification covers the design and construction of field glasses1 types ,a and ,b1 each having two powers as hereinafter specified4 #b4 ,sample4--,the bidder shall furnish with his proposal a sample of the glass which he will supply1 and award will be made after comparison of the samples with models on file in the office of the ,chief ,signal ,officer4 ,the maker will be allowed to examine the model glasses in detail in the office of the ,chief ,signal ,officer of the ,army1 ,washington1 ,d4 ,c4 #c4 ,inspection and test4--,when the order under this specification is complete1 the contractor will notify the ,chief ,signal ,officer of the ,army1 who will cause an inspection to be made4 ,it shall be the duty of the contractor to remedy any defects pointed out by the inspector1 and the contractor will be held accountable for any imperfections which the inspector may have overlooked4 ,illustration3 ,,fig4 #cd4--;,field glasses1 ,types ,c and ,d4 ,the ,chief ,signal ,officer of the ,army reserves the right to inspect any or all processes of manufacture1 and unsatisfactory material will be marked for rejection by the inspector before1 during1 or after assembly1 as occasion may arise4 ,each glass will be tested for power1 field1 definition1 and light4 ,any glass which is not the equal of the sample and model in all respects will be rejected4 ,the properties above enumerated will be tested as follows3 7a7 ,power3 ,in testing for power the glass will be placed upon a firm support about the height of the eye and directed upon a range rod1 accurately divided into divisions of #a foot1 with alternate divisions colored red and white1 respectively4 ,the rod should be placed approximately #ajj feet from the glass in a good light and with strongly contrasted background4 ,the rod is observed through the glass with one eye and at the same time with the other eye unaided4 ,an accurate comparison of the two images by means of the rod scale determines the magnifying power of the glass4 7b7 ,field3 ,the field will be determined by the use of a transit or any other instrument adapted to the measurement of horizontal angles4 ,the glass will be placed upon the telescope of the transit in such a way that the axes of collimation of the telescope and field glass barrels are parallel4 ,the extreme limits of the field of view of the glass are marked in a convenient way and the horizontal angle of view accurately measured with the transit4 7c7 ,definition3 ,in determining the definition of the glass expressed in units 7seconds7 a target will be provided with a number of lines one-tenth inch thick with one-tenth inch spaces between them drawn on a piece of heavy white paper4 ,at a certain distance this target will appear uniformly gray when viewed through the glass4 ,the inspector will gradually approach the target1 focusing the glass until he reaches the most distant point from the target where the uniform field ceases and the black and white intervals appear distinct and defined4 ,assume the distance thus found to be #bj yards and the thickness of the lines and intervals between them one-tenth inch4 ,the circumference of a circle with a radius of #bj yards or #g1bjj tenths inches is #ad1djj by #c4adaf1 or #de1bdj tenths inches2 but a circumference equals #cfj1 or 7#cfj by #fj by #fj7 #a1bif1jjj seconds4 ,if1 therefore1 #de1bdj tenths inches correspond to #a1bif1jjj seconds1 then one-tenth inch equals #a1bif1jjj divided by #de1bdj1 or #bh4f seconds4 ,the definition is therefore #bh4f seconds1 or practically half a minute4 ,the definition should be as follows3 ,for #f4e power glass #cj seconds4 ,for #e4e power glass #ce seconds4 ,for #d4e power glass #dj seconds4 ,for #c4e power glass #ee seconds4 7d7 ,light3 ,the light of a field glass is expressed by a number which is the ratio of the amount of light which reaches the eye through the glass to the amount which enters the eye unaided4 ,this comparison will be reached by means of the absorption apparatus furnished by the ,signal ,corps4 ,this apparatus consists of two wedge-shaped vessels made of brass with glass windows in the sides1 and are filled with a perfectly black liquid4 ,the sky line is first viewed through the apparatus with the naked eye and the instrument adjusted to limit of visibility4 ,the reading of the scale is then noted4 ,the sky line is again observed1 using the glass1 but in other respects as before1 and a second scale reading obtained4 ,the ratio of these readings measure the illuminating power of the glass which must conform to the standard sample4 #d4 ,service field glass1 type ,a4--7a7 ,this glass shall conform in general to the model1 now on file in the office of the ,chief ,signal ,officer at ,washington4 ,the arrangement for changing automatically from the low power to the high power1 and vice versa1 by the interposition of the plus lens at the proper distance in front of the eyepiece1 must be strictly adhered to4 7b7 ,the low power shall be approximately #c diameters and the high power shall be approximately #e diameters4 ,the figure of merit given by multiplying the numbers of diameters power by the number of degrees of field will be considered in the examination of samples1 along with the other properties of light1 sharpness of definition1 and general excellence4 7c7 ,the tubes1 frame1 and metal fittings shall be of aluminum or an aluminum alloy1 with the exception that such metal parts as in the opinion of the maker require greater strength may be made of brass4 ,tubes shall be held firmly in the frame1 single draw1 the draw action to be through a bearing surface of at least five-eighths of an inch of best black felt1 perfectly fitted so as to preserve perfect alignment4 ,the exterior metal parts1 except where leather covered1 must be given the best and most durable1 lusterless black finish4 ,the tubes and shades will be neatly covered with best quality tanned calfskin1 the leather to be sewed on1 and the seams to lie flat next to the focusing standard4 ,the interior of all parts to be painted a perfectly dead black4 ,the sunshades1 when drawn out1 shall project at least five-eighths of an inch and not over #a inch beyond the edge of the cell4 ,the focusing screw and standard should follow closely that of the sample1 except that the milled focusing disk should have a face as nearly one-half inch wide as possible and the milling should be sharper4 ,in addition to the diaphragm upon which the automatic lens is mounted1 there shall be two diaphragms in each tube1 so situated and so proportioned as to cut off all stray light and all internal reflections4 ,the crossbar supporting the draw tubes should be shaped and engraved exactly as found in the model4 7d7 ,the lenses must be entirely free from mechanical defects1 such as specks1 air bubbles1 etc42 must be free from interior strain1 and must be ground from the best obtainable glass for the purpose1 selected for general transparency1 as colorless as possible1 perfectly ground and polished1 and accurately centered4 ,the object lenses shall be composite1 achromatic1 and well corrected for spherical aberration1 with a clear aperture of at least #a inches1 and not exceeding #a-e_/h inches4 ,bidders will state the number and shape of the pieces used to make up this lens4 ,the compound lenses may be either cemented together with ,canada balsam1 or left uncemented1 as the maker may deem best for durability and optical performance1 but if left uncemented the components shall have a permanent mark to indicate their proper positions in the cell4 ,the eyepieces shall consist of a single double concave lens having a clear aperture of not less than three-eighths of an inch and not more than one-half of an inch4 7e7 ,the sling cord attached to eyes in the frame by means of brass snaps with black burned finish shall be round and braided from four strands of pliable tan leather1 and shall have a diameter of at least one-eighth of an inch and not over one-sixth of an inch4 7f7 ,the case and strap must be exactly like sample1 and of ,no4 #a stock4 ,care must be taken to put in only compasses that are in perfect condition4 ,the strap buckle must be of brass4 ,the glass1 when closed1 must not exceed #d inches in length1 and the glass1 case1 cord1 and strap1 complete1 must not exceed #be ounces in weight4 7g7 ,the frame shall be constructed with jointed bars for interpupillary adjustment4 #e4 ,service field glass1 type ,b4--7a7 ,the requirements of part #d1 service field glass1 type ,a1 of this specification1 shall be followed in the design and construction of the type ,b glass in so far as applicable4 7b7 ,power3 ,the lower power shall be approximately #d and the high #f diameters4 7c7 ,object lenses3 ,these shall have a clear aperture of at least #a inches diameter4 7d7 ,case3 ,case and carrying strap shall be furnished as required in part #d of this specification4 7e7 ,this glass shall be constructed with jointed bars for interpupillary adjustment4 7f7 ,the sunshade1 when drawn out1 shall project not less than three-eighths of an inch and not more than #a inch beyond the edge of the cell4 #f4 ,marking4--,glasses furnished under this specification shall be marked on one barrel with the words ,signal ,corps1 ,u4 ,s4 ,army1 and on the other barrel ,serial ,no4 ----4 ,serial numbers will be furnished with the order4 ,if not furnished the contractor at the time the order is placed1 the ,disbursing ,officer of the ,signal ,corps should be called upon for same1 and the numbers and other marking placed on the glasses prior to the delivery of the order4 ,,james ,,allen1 ,brigadier-,general1 ,chief ,signal ,officer of the ,army4 ,,signal ,,office1 ,electric and ,telegraph ,division4 99 99 99 99 99 ,transcriber's ,notes3 ,there is no figure #be in this text4 ,the numbering goes from figure #bd to figure #bf4 ,page #bc1 porportions changed to proportions 7in proper proportions7 ,page #ajf1 engineeer changed to engineer 7a ,french engineer7 ,page #abf1 opening bracket added to subtitle 7,revised ,february #aj1 #aiaj47