58 



SCIENCE. 



[Vol. XV. No. 364 



SCIENCE: 



A WEEKLY NEWSPAPER OF ALL THE ARTS AND SCIENCES. 



PUBLISHED BY 



N. D. C. HODGES. 



47 Lafayette Place, New York. 



Subscriptions. — United States and Canada i§3.5o a year. 



Great Britain and Europe 4.50 a year. 



Communications will be welcomed from any quarter. Abstracts of scientific papers 

 are solicited, and twenty copies of the issue containing such will be mailed the author 

 on request in advance. Rejected manuscripts will be returned to the authors only 

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 not necessarily for publication, but as a guaranty of good faith. We do not hold our- 

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 correspondents. 



Attention is called to the "Wants" column. All are invited to use it in soliciting 

 information or seeking new positions. The name and address of applicants should be 

 given in full, so that answers will go direct to them. The " Exchange " column i • 

 likewise open. 



NEW YORK, January 24, 1S90. 



No. 364 



A Steel Pressure-Blower 49 



The Tobacco-Plant 49 



What Stanley has done for the 



Map OF Africa 50 



Useful Plants in Guatemala 55 



Health Matters. 



The Blood in Phthisis and Cancer. 56 



The " Normal" Diet 56 



Tolerance of Operations on the 



Liver 56 



Leprosy Here and Elsewhere 56 



Phthisis in High Altitudes 56 



Notes and News 56 



The FiSKE Range- Finder 58 



CONTENTS 



Boo 



Reviews. 

 The Chemistry of Photography. . . . 



Evolution 



An Appeal to Pharaoh 



The Psychology of Attention 



Among the Publishers 



Letters to the Editor. 

 Physical Fields Nelson IV. Perry 

 The Orthography of " Alleghany ' 

 yacgices IK Redway 

 Mocking-Birds' Phrases 



A. Melville Bell 

 Musical Flames T. Berry Smith 



THE FISKE RANGE-FINDER. 



It has long been recognized as a prime necessity of effective 

 gunnery at sea that the gunners shall know at each instant the ex- 

 act distance of the ship or object at which they are to shoot. To 

 realize this, we must reflect, that, if two ships are approaching each 

 other at the rate of even twelve knots each, their distance apart is 

 ■changing at the rate of 13^- yards per second. This means that in 

 less 'than 4 seconds the distance or range will change 50 yards, 

 which represents the distance apart of two consecutive graduations 

 of the sight-bar of a modern rifle-gun : in other words, the sight- 

 bars of high-powered guns are usually graduated to 50 yards, and 

 it is necessary for effective shooting that an error of 50 yards must 

 not be made in estimating the distance and timing the discharge of 

 the gun as the ship rolls from side to side. But if this change of 

 50 yards be made in 4 seconds, it is plain that we must have an 

 instrument that will give the range with less than 4 seconds' delay, 

 and give it, at the very least, with less than 50 yards error. Such 

 an instrument is called a " range-finder." A description of a new 

 and exceedingly clever, as well as thoroughly scientific device, for 

 ascertaining the range and position of distant objects, designed by 

 Lieut. Bradley Allan Fiske, forms the subject of this article. 



The invention consists of a new method of finding the range and 

 position of a distant object, which depends upon the determination 



of a fractional portion of a conducting body bearing in length a 

 ratio to the angle included between two lines of sight directed upon 

 said distant object and the measurement of the electrical resistance 

 of said length. 



The accompanying drawings are (Fig. 4 excepted) all electrical 

 diagrams, not drawn to scale, and symbolically represent the in- 

 vention. In Fig. I is shown a Wheatstone bridge, in one member 

 {a) of which is arranged a body of conducting material in arc form, 

 and a movable arm traversing the same. In Fig. 2 is shown a 

 Wheatstone bridge having arcs and movable arms arranged in two 

 members, a b. In Fig. 3 is shown a Wheatstone bridge in which 

 arcs connect adjacent members, a.s a c and i> d, and movable arms 

 sweeping over said arcs are connected' to the battery. Fig. 4 is a 

 mathematical diagram illustrating the method of determining the 

 angle ATC. Fig. 5 shows a disposition of the range-finder in con- 

 nection with a dead-beat galvanometer; and Fig. 6, the same in' 

 connection with the slider. Similar letters of reference indicate 

 like parts. 



In Fig. i,\t\. a b c d represent the four members of an ordinary 

 Wheatstone bridge, and^^^ the transverse member, in which is con- 

 nected the galvanometer g' . A battery / is also connected to the 

 bridge in the usual way. In the members c and d are placed the 

 fixed resistances c' and d', and in the member b the variable re- 

 sistance b' also, as usual. One wire from battery/, however, con- 

 nects to the end of member t:, and also to the pivot / of a swinging 

 arm z. The extremity i of arm z' moves over and maintains elec- 

 trical contact with an arc /i of conducting material, which has one 

 extremity j connected, as shown, to the member a of the bridge. 

 It is obvious that when the arm z' is in the position shown in full 

 lines in Fig. i, then the current will traverse the whole arc A ; and 

 when said arm is in the position indicated by dotted lines (Fig. i), 

 then the arc A will be cut out, and the current will pass directly to 

 member a. Now assume the arc /i to be made of such material, 

 and so proportioned that its electrical resistance to a current travers- 

 ing it will be proportional to the length of arc included between the 

 contact end k of arm z' and the connecting-point J of member a 

 with said arc. Therefore the resistance interposed in the member 

 a of the bridge will be commensurate with the angle/ I i ; and if 

 this resistance be known, the angle is also known. Let it now be 

 assumed that the galvanometer £■' and variable resistance b' be 

 located at some point distant from the moving arm z', from which 

 said arm is invisible or inaccessible. Clearly, then, an observer 

 stationed at the galvanometer £■' and resistance b' can, by noting 

 the galvanometer and adjusting the resistance in the usual way, 

 determine the resistance equilibrating any position of arm z' along 

 the arc A, and so discover the angle of adjustment of said arc ; or, 

 having adjusted the resistance b' at some given figure, the observer 

 may, by simply noting the galvanometer or any other suitable indi- 

 cating device, visual or audible, determine when the arm z is placed 

 at a desired angle corresponding to the adjusted resistance, and 

 this indicating device may obviously be at the place where the 

 moving arm is- located, so that the operator there may thus know 

 when he has placed the arm at the predetermined point or at the , 

 distant station, so that the operator in charge of the resistance b' 

 may know that the arm has been adjusted properly ; or two indi- 

 cating devices in the same circuit may give warning to both 

 operators, as above, simultaneously. 



Referring now to Fig. 2, it will be apparent, that, in lieu of the 

 variable resistance b' in the member b, there is arranged an arc 

 A' and swinging arm z'. Tbe arc // is connected at one end J' to 

 the member b, and the swinging arm z'' makes contact at one end 

 A' with said arc, and to its pivot /' is connected the member d. 

 The arrangement and construction of arc A' and arm z' are similar 

 to those of arc A and arm z: consequently, when the arm z' is set at 

 a certain point on the arc A, the arm z' must be set at the corre- 

 sponding point on the arc A', in order that the resistance of the 

 lengths of the arcs A A' respectively between the point k and point 

 A and point k and point A' may balance ; hence, if the arm k be set 

 at a certain angle, the observer at arm k may recognize that angle 

 by noting the position of the arm k and the galvanometer, as be- 

 fore. It will be observed, however, that the effect of moving the 

 arm z over arc A is practically to lengthen or shorten or to inter- 

 pose more or less resistance in the member a of the bridge, and by 



