January i6, 1902] 



NA TURE 



261 



work than elaborately fitted laboratories. Desk work must be 

 dethroned to a large extent and the pupils be given more time 

 in the open air. 



The exhibition of home-made apparatus was not so good as 

 usual this year. Judging from the remarks of many teachers 

 present at the conference, this exhibition has in previous years 

 been regarded as one of the most helpful of the items on the 

 programme of events, and Dr. Kimmins, to whose energy the 

 success of the conferences is due, should develop this side of the 

 annual meetings as largely as possible in future. 



A. T. Simmons. 



A NEW RANGE-FINDER.^ 



T^HE instrument designed by Prof. Forbes is intended only 

 ■*• for use with rifle fire. It is not suitable for long-range 

 artillery, or for the Navy. This infantry type is by far the 

 most difficult to produce, because, in addition to accuracy, 

 extreme portability is an essential feature. At the same time, 

 the infantry are more in need of some addition to their present 

 resources than any one else, and the urgent need of such an 

 instrument has been proclaimed and re-echoed by all our 

 officers who have returned from the war in South Africa. 



All methods of optically measuring the distance of an in- 

 accessible object depend on using a base 

 of known length, which must be measured 

 on the ground, or else be part of the in- 

 strument. In the latter case the instrument 

 can usually be worked by one man, who 

 can find the distance without changing his 

 position. This class of instrument is some- 

 times spoken of as short-base range-finders. 

 Numerous patents for such instruments 

 have been applied for ; but the difficulties 

 in the way of ensuring accuracy are so 

 great that only one type has ever been 

 perfecf"! and generally used. The Barr 

 and Stjoud range-finder has been adopted 

 by the Navy with most satisfactory results, 

 and this has proved the fact that a short 

 base (4i feet) is not inconsistent with 

 accuracy. For the use of infantry, how- 

 ever, where extreme probability, and 

 accuracy, and suitability for ill-defined 

 objects, such as men, bushes, rocks, &c. , 

 are essentials, this is an unsuitable instru- 

 ment. 



In the Barr and Stroud instrument the 

 two images of a distant object are seen 

 with one eye, hence the object appears 

 to be double until the micrometer arrange- 

 ment has been so moved as to make a 

 coincidence of the two images, when the 

 scale reading of the micrometer gives the distance directly. 

 Now in naval work, for which this instrument is made, a ship, 

 or its mast or funnel, is very sharp against the sky, and the 

 coincidence can easily be made ; but this method is almost 

 valueless in the field. A bush, or a rock, or a man is an object 

 so ill-defined, especially against certain backgrounds, that in 

 attempting to make a coincidence you may move one picture 

 in the telescope over the other for a considerable angle before 

 you are sure that it is double. The difficulty has been got 

 over by Messrs. Carl Zeiss and Prof. Forbes, who make use of 

 stereoscopic vision in the new range-finder. 



The instrument consists of a lolding aluminium base, 6 feet 

 in length, and a field glass. The base is a square tube hinged 

 at its middle, and folds up to 3 feet 6 inches. Each half has 

 at each end a doubly reflecting prism. The rays of light from 

 a distant object strike the outer pair of these four prisms, are 

 reflected at right angles along each tube, and are then reflected 

 at the two middle prisms into the two telescopes of the binocular 

 fixed to the base, in directions parallel to the original rays 

 intercepted by the outer prism.s. It is the measurement of the 

 angle between these rays that tells the distance of the object 

 looked at. This angle is measured by two vertical wires, one 

 in each telescope, seen by the two eyes. One of the wires is 

 fixed, the other is moved by a micrometer-screw until the two 

 t Abstract of a paper read before the Society of Arts on December 18, 

 1901, by Prof. George Forbes, F. R.S. 



wires appear as one, while the object is seen distinctly. This 

 gives the distance accurately to 2 per cent, even at 3000 yards. 

 But now stereoscopic vision comes in and gives far greater 

 accuracy. The wire seems to stand out solid in space, and the 

 slightest turn of the micrometer screw causes the wire to appear 

 to be nearer or farther than the object looked at, and when the 

 wire appears to be at exactly the same distance the micrometer 

 reading gives the distance with an accuracy far greater than 

 that attainable by observing the duplication of images on the 

 retina. 



This range-finder can be used in a variety of positions. The 

 more steadily it is held the more accurate the result. A stand- 

 ing position is the least steady. When kneeling, using only 

 half the base, the other half may be bent down at right angles, 

 and so form a leg which serves as a rest on the ground. The 

 most easy position is sitting with the elbows resting on the 

 knees. Another steady position is lying flat on the ground 

 facing the object (Fig. i). In every one of these positions you 

 can take advantage of cover. Since the eyes are virtually at the 

 extremities of the base, the observer may stand, sit, kneel, or lie 

 behind a tree, bush, rock, ant-hill, horse, comrade, or waggon, 

 and will not only be more able to work without sensation of 

 danger, but without drawing the fire of the enemy on his 

 comrades. 



Lord Kitchener having expressed a desire to see the range- 



FlG. I.— Range-Finder in use behind cover. 



finder tested in the field. Prof. Forbes has proceeded to South 

 Africa with his instrument, and a thorough examination of its 

 efficiency will be made under practical conditions. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



The Prince of Wales having consented to be nominated as 

 Chancellor of the University of Wales, has been elected to that 

 oflicc in succession to His Majesty the King, who has assumed 

 the title of Protector of the University. 



The executive committee of the Carnegie Trust met at Edin- 

 burgh on Monday. The secretary and treasurer submitted their 

 reports for the period ended December 31, 1901, showing that 

 fees have been paid by the Trust to 2441 students, amounting to 

 the sum of 22,941/. ids. 6J. It was arranged to hold the annual 

 meeting of the trustees in London, at which the first report of 

 the executive will be submitted. 



At a special meeting of the Governors of University College 

 Dundee, on January S, Sir W. O. Dalgleish intimated that he 

 would provide a sum of 5000/. for the building of the new 

 medical school, and an additional sum of 5000/. towards the 

 extinction of the debt on the College. This latter sum will be 

 payable only if within a certain reasonable time sufficient money 

 is subscribed to make up the remaining sum, the balance of 



NO. I 68 I, VOL. 65] 



