March 9, 1899J 



NA TURE 



437 



properly to Tycho. But we should imagine him to be a 

 greater than Tycho, for without the same assistance, 

 without the encouragement of kings and the applause of 

 his fellows, he has advanced his favourite science quite 

 as effectually as did the Danish astronomer. It is espe- 

 cially curious to notice that the system at which Chan- 

 drasekhara ultimately arrived, and the explanation he 

 offers of it, bears a very considerable resemblance to that 

 which Tycho taught. The author has never been able 

 to convince himself that the earth turns on its a.xis, or 

 that it goes round the sun ; but to the planets he assigned 

 heliocentric motion, much as Tycho did. 



We get some notion of the success that attended the 

 work, and of how much it is in one man's power to ac- 

 complish, if we examine the differences between the 

 values he assigns to some of the constants of astronomy 

 and those in use with ourselves. The error in the 

 sidereal period of the sun is 206 seconds ; of the moon, 

 I second ; Mercury, 79 seconds ; Venus, about 2 minutes ; 

 Mars, 9 minutes ; Jupiter, an hour ; and Saturn, rather 

 more than half a day. The accuracy with which he 

 determined the inclination of the planets to the ecliptic 

 is still more remarkable. Mercury offers the largest 

 error, and that is only about two minutes. In the case 

 of the Solar orbit the greatest equation to the centre is 

 only 14 seconds in error. In the Lunar theory, the 

 revolution of the node has been concluded with an error 

 of about 5! days, less than the thousandth part of the 

 ,vhole period ; while he has independently detected and 

 assigned very approximate values to the evection, the 

 variation, and the annual equation. 



The main object that Chandrasekhara had before him 

 seems to have been to correct the calendar, and regulate 

 the daily ritual of the Hindu religion. No two almanacs, 

 Prof. Ray tells us, agree ; but any attempt to introduce 

 the Nautical Almanac and its acknowledged accuracy 

 would prove unsuccessful. The necessary corrections and 

 unification must, to be acceptable, come from within and 

 be the work of a Hindu, uninfluenced by foreign educa- 

 tion. The work of Chandrasekhara has received the 

 sanction of the honoured Rashis, and the adoption of 

 the corrections vv'hich he has shown to be necessary will 

 exert upon native society a beneficial influence, whose 

 importance can be hardly overrated in a community 

 where a correct almanac is an indispensable equipment 

 of every household. We should like much to linger over 

 Prof Ray's remarks on the subject of precession and his 

 chronological deductions. These and many other points 

 are discussed with great ability, though Prof. R<iy 

 modestly disclaims any special astronomical capacity. 

 The effect is to leave us at every page with a higher 

 opinion of the author laboriously recording his observa- 

 tions on a palm-leaf, and unselfishly devoting his life to 

 the services of his countrymen, who do not appreciate 

 the nobility of the effort and the entirety of his devotion. 

 We are in full sympathy with the editor when he writes 

 thus of the author, of his privations and his star-gazing : 



"What has he done after all ? asks the impatient critic. 

 To him I would say — Is it not enough to find in this 

 man a true lover of science, who, regardless of other 

 people's unfavourable opinion of his work, their taunts 

 and dissuasions, has devoted his whole life to the one 



NO. 1532, VOL. 55] 



pursuit of knowledge ; who has shown the way to original 

 research amidst difficulties serious enough to dishearten 

 men in better circumstances ; who has employed his 

 time usefully, instead of frittering it away like the usual 

 run of men of his rank, on a work which guides the 

 daily routine of millions of his countrymen." 



^ W. E. P. 



UUR BOOK SHELF. 



Photography: its History, Processes, Apparatus, and 



Materials. By A. Brothers, F.R..'\.S. Second Edition. 



Pp. xviii -V 367. (London : C. Griffin and Co., Ltd., 



1899-) 

 Mr. Brothers, of Manchester, has been known for so 

 many years in connection with photography and allied 

 subjects, that his personal experiences have much value 

 for the student. The time is gradually approaching 

 when the history of the early developments of photo- 

 graphy will be completed, because it will be impossible 

 to add to our recorded knowledge of them ; meanwhile 

 we welcome every addition. Mr. Ikothers describes 

 the first experiments in the use of magnesium as an 

 illuminant for photographic purposes, and how he found 

 that the wire burned better when it was flattened into 

 ribbon by passing it between rollers. The first photograph 

 taken underground was by Mr. Brothers, and he gives a 

 reproduction of it. It was produced in 1864 in the Blue 

 John Mine in Derbyshire, by the aid of burning mag- 

 nesium. In the following year Prof Piazzi Smyth used 

 the same illuminant in photographing the chamber in the 

 interior of the Great Pyramid. Being in doubt as to who 

 was the first to use sodium thiosulphate as a fixing reagent, 

 Mr. Brothers, in 1866, wrote to Sir John Herschel, 

 and received from him a long letter on the subject, which 

 is printed in full in the work before us. In it Sir John 

 gives quotations from his papers on "hyposulphurous 

 acid and its compounds," published in the Edinburgh 

 Philosophical Journal of 18 19, and also extracts from 

 his own laboratory note-book of January 1839, which 

 appear to establish his claim to being the first to use the 

 thiosulphates in photography. The description of Sir 

 John's attempts to imitate the photographic successes of 

 Daguerre, of which at that time there were only very 

 vague reports as the process was not published until 

 later in the year, are very interesting. 



Although the volume is called a " Manual of Photo- 

 graphy," it is hardly what is commonly understood by 

 this term. .After introductory matter, which is chiefly a 

 consideration of chemistry, optics, and artificial light, as 

 applied in photography, there follow sections titled 

 " Processes," " Apparatus," " Materials used in photo- 

 graphy," " Applications of photography," and " Practical 

 hints." In each section the numerous headings are 

 alphabetically arranged, their descriptions extending 

 from two or three lines to, occasionally, several pages 

 in length. The space allotted to each subject is not 

 proportional to its demands. While more than eight 

 pages are devoted to the stereoscope, less than three are 

 given to carbon printing, and for details of this most 

 important of processes the student is referred to the 

 guide issued by the Autotype Company 1 This bemg a 

 second edition, much new matter has been added. 

 Radiography, the "krornoscope," the new developers, 

 and some of the newer lenses are described, the last 

 chiefly by quotations from the makers' price lists. The 

 greatest advance in photographic optics since Petzval 

 calculated the portrait lens that bears his name, is prac- 

 tically ignored. Astigmatism is referred to, in a dozen 

 lines or so, as "a defect most general in portrait lenses" 

 that "has to be reduced to a minimum by the use of a. 

 diaphragm." It is worth noting that at both pages 



