July 30, 190S] 



NATURE 



Methods of Surveying. A Manual for Students, 

 Estate Ag-ents, and Planters. By N. F. Mackenzie. 

 Pp. ix+143; illustrated. (London: Bradbury, 

 Agnew and Co., Ltd., igoS.) 

 Written by a practical surveyor and teacher, this 

 manual is just what is required by the bef^inner, be 

 he student or practitioner, in surveying-. It contains 

 just what is necessary and little that is superfluous; 

 each step is so clearlv indicated, and the little prac- 

 tical hints given are so apt, that a novice could go 

 straight on with his work with only the manual to 

 guide him; but a knowledge of plane geometry, 

 trigonometry, and drawing is assumed. The book is 

 only intended for teaching the methods emploj'ed in 

 making large scale plans of comparatively small 

 areas, therefore the methods of the trigonometrical 

 survev and geodetic work are not given. The author 

 <leals in turn with chain surveying, prismatic com- 

 pass surveys, theodolite traverses, levelling, plane 

 table operations, and the determination and plotting 

 of contours. Interspersed are chapters describing the 

 various instruments, each of which is carefully ex- 

 plained in detail with the help of numerous photo- 

 graphs and diagrams. Problems are set and solved, 

 and practical methods of overcoming incidental 

 difficulties in the field are dealt with. ."Xs an example 

 of the thoroughness with which each essential point 

 is treated, one might take p. 21, where all the con- 

 ventional signs employed to denote various objects 

 shown on the finished plan are not only explained, but 

 are also reproduced, and this is but one example 

 among the many that this excellent manual contains. 

 For teachers who have the desire, and are in a position, 

 lo teach real, practical geography, the book is the 

 best we have yet seen. W. E. R. 



A Guide lo the Domesticated Anivials (other than 

 Horses) exhibited in the Central and North Halh 

 of the British Museum {Natural History). Pp. vi + 

 54; illustrated by 24 figures. (London: Printed by 

 Order of the Trustees of the British Museum, igoS.) 

 Price 6d. 

 Dr. R. Bowdi.er SriARPE states in a preface that this 

 very attractive guide has been written by Mr. R. 

 Lydekker, F. R.S., which is guarantee enough of its 

 accuracy and completeness. The interest of the collec- 

 tion here dealt with to breeders, fanciers, and the 

 public generally is self-apparent. .Accompanied by 

 such a guide as this little book provides, any intelli- 

 gent person will be able to understand the principles 

 exemplified by the specimens described. The excel- 

 lent plates will make the book useful also to students 

 unable to visit the museum. 



LETTERS TO THE EDITOR. 



[Tile Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with tile writers of, rejected 

 manuscripts intended for this or any other part 0/ Nature. 

 No notice is taken of anonymous cotnmunications.] 



The Isothermal Layer of the Atmosphere. 



In Nature of March 12, p. 437, I made some remarks 

 under the above heading on temperature observations in 

 the upper atmosphere, and suggested that it was desirable 

 to have simultaneous records from thermographs of the 

 different types in use in this country and abroad. From 

 " Heft 2, Jahrgang 1907, of the Beob .... mit . . . . 

 Ballons . . . ." recently published under the editorship of 

 Prof. H. Hergesell, I find that the desirability of such 

 comparisons had already been recognised on the Continent. 

 There are only two or three CNamplcs of such comparisons 

 in the volume, but tliey illustrate in a remarkable fashion 

 the uncertainties which I was led to anticipate from general 

 considerations. The thermographs compared were of two 



types — .\ (that of Monsieur Teisserenc de Bort), B (that 

 of Prof. Hergesell). 



Taking first Strassburg, we have data for the ascents 

 only, on February 7 and 8, 1907. On February 8 the 

 differences between A and B varied from 00 C. to 2°.i C. 

 in a total range of 52° C. In this case A gave, with 

 one e.xception, the higher temperature, so the difference 

 may have been partly due to " zero error " in one or 

 both of the instruments. On February 7, as the balloon 

 rose, the temperature recorded by A fell from — 3°-4 C. 

 at 140 metres to — 6o°-2 at 9280 metres. B, originally 

 in agreement with .\, gradually began to read lower, the 

 difference amounting to i°-8 when A recorded — 34°-2. 

 The difference then diminished, being only 1° C. when .'\ 

 recorded — 6o°-2. There then followed a thin isothermal 

 layer, followed, as usual, by an inversion of temperature 

 (a phenomenon not uncommon at comparatively low levels), 

 but while A's temperature rose from — 6o°-2 to — s8°.3 (or 

 i°-9 C), B's only rose from — 6i°-2 to — 6o°-7 (or o°-5 C). 

 The instruments then differed by 2°-4 C, and shortly after, 

 when the ascent stopped — the temperature then being 

 -53"- 1 C— by 2''.5 C. 



When .•\, with falling temperature at 9140 metres, showed 

 — 58°-8, B read only i°-2 lower, but when, after the in- 

 version of temperature, A showed — 58°-3 at 0690 metres, 

 B road 2°-4 lower. There is thus in this case something 

 quite different from mere zero or scale error. The cause 

 must have been in the type or construction, or in the 

 exposure of the instruments. 



.-\ still more instructive case is presented by the 

 results obtained at Uccle on February 7, 1907, with 

 the same two types of instruments ; in this instance 

 the observations are recorded during both ascent 

 and descent. During the ascent the differences between 

 .\ and B varied only from — o°-6 to -hi"-! C. As tem- 

 perature fell to —42°, B usually read lower by a few 

 tenths of a degree ; at greater heights B read higher by 

 from o°-2 to i°-i. During the descent, however, a marked 

 difference of a systematic kind appeared, B reading higher 

 than .\. The maximum difference 2°-9 C. appeared when 

 A recorded —^6°-$, in spite of the fact that when A 

 recorded — 46°-3 during the ascent, B differed by only 

 o°-2. .As the descent continued, the difference between 

 .\ and B diminished and changed sign, until when A 

 showed — 8°-9, B read i°-6 lower. Between the heights 

 of 6000 and 1 150 metres, when the extreme differences 

 between .\ and B occurred, we have a range of 37°-6 from 

 A as against 33°-! from B, a difference of 4°-.=i C, or 

 about 12 per cent. On this occasion- there was a marked 

 inversion of temperature near the highest level attained, 

 but the conclusions one would draw as to the nature or 

 even as to the existence of an isothermal layer of finite 

 thickness would depend a good deal on whether one took 

 the ascending or descending readings, and in the latter 

 event on whether .\ or B was accepted as correct. Thus, 

 while A during the descent gave the same reading { — 62°-^) 

 at 9000 as at 10,090 metres, B read higher by 2°-2 at the 

 lower level. Both at Strassburg and Uccle the differences 

 between A and B became accentuated when temperature 

 inversion occurred. So decided was the instrumental in- 

 fluence that in the short abstract accompanying the Uccle 

 figures the writer speaks of " isothermie au T. de B." 



In making these and previous comments, mv object is 

 not to criticise directly or indirectly any particular type 

 of instrument, or any one observer or class of observers, 

 but solely to secure the adequate and timely recognition 

 of an idea, that idea being that no reasonable precaution 

 should be omitted to ascertain how different types of 

 meteorographs stand to one another, and how their records 

 may best be interpreted. C. Chree. 



July 18, 1908. 



The Nature of the 7 and X-Rays. 



'liiE arguments contained in Dr. Barkla's letter to 

 Naic/RE ot May 7 do not directly affect the position which 

 I have taken in respect to the nature of the 7 and X-rays. 

 I have shown that all the striking phenomena of the 

 secondary kathode radiations are simply and completely 

 explained on a neutral pair theory, but not on the older 

 theory of ether pulses. Dr. Barkia refuses to consider this 

 large body of evidence on the ground that it is well to 



NO. 2022, VOL. 78] 



