576 



NA TURE 



[October io, 1901 



acquaintance with the subject is ensured. There is, 

 perhaps, no department of farming which suffers so much 

 from mismanagement as the poultry yard, yet the industry 

 is of national importance. Mr. Watson reminds his 

 readers that the annual value of farm poultry and eggs 

 produced in the United States, according to the census 

 returns of 1S90, exceeded the annual value of the coal, 

 iron, and mineral oil produced during the same period. 

 In England we have no such statistics, but the Trade 

 and Navigation Returns show that the imports of poultry 

 and eggs to this country amounted last year to the value 

 of 6,416,46s/. The book has numerous illustrations. 



K. W. 



The Collected Scientific Papers oj John Couch Adams. 

 Vol. ii. Pp. xxxii + 646. (Cambridge University 

 Press, 1900.) 



The astronomical papers in this volume have been ably 

 edited by Prof. Sampson. The first eighteen papers 

 form a connected series on the lunar theory, and are 

 substantially the lectures on that subject which Adams 

 used to deliver at Cambridge. As an aid to the student 

 they probably surpass any text-book that has been 

 written on the subject. It has been said that the diffi- 

 culties of the lunar theory begin where the text-books 

 usually leave off, but Adams introduces the reader to 



LETTERS TO THE EDITOR. 



\The Edltoy does not hold hiinsetf responsible for opinions ex-' 

 pressed by his correspondents. Neillter can lie uiiderlal;e 

 io return, or to (Oi respond with the writers of, reje el 

 manuscripts intended /or this or any other part of Natuke. 

 Ao notice is taken of anonvmous communications.'^ 

 The Rolling Angle of a Ship found by Photography. 

 While crossing the Pacific Ocean between Auckland, N.Z., 

 and Sydney, N. S.W., in the Union s.s. Mokoia, I wished to 

 determine, if possible, the rolling angle of the ship by some 

 means, other than that of the inclinometer, which the captain 

 allowed me to inspect from time to time. As the period of 

 rolling was long, it seemed quiie possible that an ordinary 

 kodak camera might be manipulated and a fresh film intro- 

 duced, between the end of the roll to port and then to starboard. 

 This turned out to be the case : the results are shown in the 

 pictures A and B, which indicate the inclination of the ship to 

 the horizon, to starboard and to port, respectively. The films 

 when developed and finished were superposed, so that the 

 pictures of the ship in each photograph coincided. The print 

 made from this combination of the pictures E and \ gives the- 

 composite picture c, in which the horizon in picture A is 

 separated from that in picture B by the angle shown, which 

 when measured with a circular protractor was found to be 

 19' 6'. After a few trials, no difficulty was experienced in 

 making the exposure at the right time, viz., at the ends of a 

 roll. Better results might have been obtained on dry plates, as 

 films do not stand high temperatures well. The film B is 



Union Steamship Co.'s Molioia. Rolling angle found by photography, a is a pictur< 

 picture taken at the instant of the end of rolling to the left, p ; c is a composite pil 

 of the ship are rnade to coincide, thus the angle between tlie two ' 

 To Sydney 325 miles. 



Ml at the instant of the end of rolling tc 

 made by superposing the two films. A 

 A and B is found. Lat. 34" 27' S. 



the right, s : b is a 



nd B. The pictures 



Long. 157° 43' E. 



many of the practical difficulties of the numerical work, 

 such as the slow convergence and small denominators. 



The other astronomical papers are miscellaneous in 

 character and must have taxed the editor to the utmost, 

 for, to quote the preface, " the papers . . . were almost 

 devoid of arrangement. ... It would have been a hope- 

 less task . . . had not almost every page been dated. 

 This permitted reference to a diary. . . ." Among the 

 most interesting papers are those on Jupiter's satellites, a 

 subject which Prof. Sampson has made his own, a paper 

 on an infinite determinant in the motion of the moon's 

 node which shows that Adams came nearer than anyone 

 else to anticipating Hill in his treatment of the lunar 

 theory, and some papers on the moon's secular accelera- 

 tion. 



The second and larger half of the volume is devoted 

 to .Adams' papers on terrestrial magnetism edited by 

 his brother. Prof W. C. .Adams. These consist chiefly 

 in a determination of the Gaussian magnetic constants, 

 a problem for which the material is even now scanty, 

 owmg to the fact that such magnetic observatories as 

 there are, are for the most part closely grouped together 

 in one portion of the earth's surface. 



NO. 1667, VOL. 64] 



very slightly distorted. The angle may also be found by means 

 of a single picture ; in this case a small stop should be used, and 

 the exposure made for a longer period than that of one roll ; 

 the angle then appears as a rather faint fan, but the definition at 

 the ends of the roll is not so well defined as when two pictures 

 are made and then superposed. 



Since my return to England, I find that M. Huet, of the Frencli 

 Navy, used a photographic method for indicating the rolling 

 angle. But as his work on the subject is only in the hands oi 

 the French Naval Department, it cannot be consulted. His 

 method is referred to in Sir \V. White's " Manual of Naval 

 Architecture." After obtaining the results shown in picture c, 

 I devised an apparatus whereby the inclinometer angle may be 

 simultaneously compared with that found by the photographic 

 method. By this means, the positions of the inclinometer are 

 also recorded on the films on which the horizon appears, so 

 that the angle shown by the inclinometer may be at once 

 compared with the angle found by the photographic method, 

 which is entirely free from the eriors inherent in pendulum 

 inclinometers. F. J. Jervis-.Smith. 



British Instruments at the Paris Exhibition. 

 In connection with the English exhibits at the Paris Exhibi- 

 tion last year, it may be worth while to quote the concluding 

 paragraph of this part of the impartial and very carefully con- 



