August io, 191 i] 



NATURE 



199 



The results given are very meagre, and are as follows :■ — 

 ["he efficiencies varied between 53 per cent, and 69 per cent, 

 ["he thrust fell off in flight about 33 per cent, from the 

 ■alue with the aeroplane anchored. The rotational speed 

 if the engine increased in flight from o per cent, to 15 per 

 rat. above the speed with the aeroplane anchored, depend- 

 ng on the propeller. The experiments are to be continued 

 vitli the aid of a further grant, and we may therefore 

 xpect more complete results of tests with the addition of 

 nore particulars of the propellers tested than are given in 

 he present article. 



It is to be hoped that the experimenters may improve the 

 iccuracy of their apparatus, so that their results may be 

 I real scientific value, and not merely for the purpose of 

 Berentiating between a good propeller and a bad one. 

 Francis H. Bramwell. 



PHOTOGRAPHY IN SURVEYING. 



COR the last half a century continued efforts have been 

 made to utilise photography in the preparation of 

 ccurate plans of country, and thereby economise some of 

 he time expended in the detailed measurement of every 

 eature and object. A photographic negative provides an 

 ccuraie record of the area included in it, contains much 

 etail which measurement alone cannot give, and is always 

 vailable for future reference. On the other hand, the 

 mploymcnt of photography requires certain technical know- 

 jdge, and a good judgment in the selection of stations and 

 iews ; it is best suited to regions of considerable relief, 

 ut even then patches of ground are liable to be omitted 

 ltogether from, the views, and such omissions are not 

 ecognised until the work is plotted; lastly, it necessi- 

 ites considerable skill in the drawing office to get 

 lie best and most complete results from the field-work, 

 'hotogrammetry has, therefore, developed most rapidly in 

 Bntries where mountainous districts offer favourable 

 onditions for its employment, and where the season avail- 

 ble for field-work is limited. France, Italy, Germany, 

 lustria, Switzerland, and Canada have all made use of 

 tfs method in topographical surveys, despite its draw- 

 acks. Mr. A. O. Wheeler * describes in general terms the 

 lethods which are employed in Canada under the direc- 

 ion of Dr. Deville, the Surveyor-General of Dominion 

 .ands, and employed by Mr. Wheeler on Dr. Longstaff's 

 scent expedition in British Columbia. But the labour 

 tvolved in utilising the information collected by the 

 amera has always hindered its wider employment in 

 Breying, so that we welcome a new method of automatic- 

 lly reproducing it on a plane surface, which is described 

 y Prof. K. Bruckner. 2 



Some years ago Dr. C. Pulfrich, of the firm of Carl 

 eiss, of Jena, produced his stereomicrometer, by which 

 le coordinates of points represented on a pair of stereo- 

 raphic plates were determined, and their positions defined, 

 J that they could be plotted on a plan. In this instru- 

 lent the plates are fixed, and the movements of the index 

 ointers are measured. A further development was the 

 :ereocomparator, in which the plates are movable, and 

 le points to be measured are brought under fixed marks, 

 I this case the objectives of a stereoscope. By suitable 

 lechanieal arrangements the coordinates of any point on 

 le picture and the stereoscopic parallax are readily deter- 

 lined, thus providing the necessary information for 

 lotting the point measured. Lieut, von Orel, of the 

 lilitary Geographical Institute in Vienna, conceived the 

 lea of automatically recording the data thus measured, 

 nd the necessary modifications have been made to the 

 :ereocomparator so as to enable the data to be plotted 

 lechanically on a sheet of paper. This instrument is 

 ailed the stereoautogrnph, and in it the movements of the 

 lates and the stereoscope of the stereocomparator are 

 immunicnted to flat rulers resting on the drawing-board, 

 nd by their aid the positions of points are plotted on the 

 Ian. Not only is the horizontal projection of the detail 

 ffected in this way, but contour lines representing the 

 ?Iief can also be drawn. 



Plans .on a scale of 1 : 25,000 can be accurately pro- 



' Geographical Journml, June. 



- Mill. ,/./.:/.: gtographischen Gtsclhchaft in Willi, Ed. 54, No. 4. 



NO. 2l8o, VOL. 87] 



duced in this way, and even one on the scale of 1 : 10,000 

 showed but slight differences from a precise measured 

 survey of the same on this scale. The apparatus is said 

 to be capable of producing a map sheet 35 cm. by 25 cm. 

 of a mountainous region to the scale of 1 : 25,000 in about 

 ten days' work, so that it promises to be of great value 

 in reproducing the work of travellers and explorers who 

 will take the necessary photographs. Photogrammetric 

 methods do not apply where surveying is organised so as 

 to utilise a personnel of moderate technical ability, where 

 each individual carries out a single stage of the work 

 only ; but where skilled technical assistance is available, 

 and each surveyor executes as complete a survey as possible 

 of a given area, then stereophotogrammetry, simplified by 

 Lieut, von Orel's instrument, seems to offer great possi- 

 bilities, especially when conditions of work and of surface 

 relief are also favourable. 



Though primarily adapted to topographical representa- 

 tion, some have tried to adapt photography to large-scale 

 (cadastral) work, and M. J. Gaultier has proposed method? 

 for its employment. But the indoor work of the necessai y 

 precision is tedious and costly, so that in a recent paper ' 

 he proposes for such work an instrument which he names 

 the " topometrographe." This is of the nature of a plane 

 table for precise work, stoutly built and carefully levelled, 

 on which a base-bar is clamped. This carries the pivots 

 of two rulers set at a distance apart corresponding to the 

 base line used. These rulers are set at any desired angle 

 with the base-bar by means of divided circles, and their 

 intersection locates the apex of the triangle. Very con- 

 siderable accuracy is claimed for the method, which is to 

 be based on a network of third- or fourth-order triangula- 

 tion ; but its effectiveness would appear to be restricted to 

 special cases, where such elaboration in the field is com- 

 pensated for by economy in the office. 



BIRD-NOTES. 

 T7ROM the point of view of forest-conservation much 

 interest attaches to Mr. F. E. L. Beal's report on 

 the food of American woodpeckers, published as Bulletin 

 No. 37 of the biological division of the U.S. Department 

 of Agriculture. The report is based on the examination 

 of the contents of a large number of stomachs of sixteen 

 species of these birds ; but since the number of specimens 

 examined was much smaller in some cases than in others, 

 it is quite probable that some modification of the order in 

 which these species are tabulated according to the nature 

 of their food may be necessary in the future. Another 

 element of uncertainty in this respect is due to the rapidity 

 with which the vegetable food of the cambium-eating 

 species passes through the stomach. 



As the forests of the United States, like those of other 

 countries, have a host of insect enemies, among which 

 wood-boring beetles are pre-eminent, any natural agency 

 that will assist in keeping these pests in check is of the 

 highest value. In the case of wood-boring beetles, wood- 

 peckers occupy the first place as destroyers, and among 

 these the two species of the three-toed genus Picoides are 

 the most valuable. In the typical P. americanus no less 

 than 94-06 per cent, of the food consists of animal matter ; 

 while as regards its insect-food, 71-05 per cent, consists of 

 beetles and the remainder of ants. Most of these beetles 

 are wood-borers, although a percentage consists of harm- 

 less species. Ants also are deleterious to trees, since they 

 often take possession of the borings from which beetles 

 have been extracted by woodpeckers, until they in turn are 

 routed out by these birds. Woodpeckers are frequently 

 charged with inflicting damage on sound trees : but the 

 charge, except in the case of the American group of sap- 

 suckers, is considered to be unfounded. As regard? 

 sapsuckers, which feed on cambium, these certainly do 

 inflict damage, which in some cases may be serious 

 although, on the other hand, they consume legions of ant'. 

 The colouring of the Tack snipe forms, according to Mr. 

 F. J. Stubbs'in The 'Zoologist for July, an absolutely 

 perfect protective adaptation. In some localities the onlv 

 means by which the bird can be detected when squatting 

 in its proppr haunts is bv looking for a couple of curved 

 blades of faded grass of a brighter hue than any indi- 

 1 Rome Scientifiqut, May 6. 



