y^dy 36, 1874] 



NATURE 



243 



an acknowledged authority, we find the number of species 

 of Rubiis increased from 41 to 45, while that of Rosa is 

 reduced from 19 to 11, and of Salix from 32 to 29. We 

 have never been able to understand on what piinciple 

 Characeaj find a place in a work devoted to " Flowering 

 Plants and Ferns," by the latter term being apparently 

 meant Vascular Cryptogams. Prefixed to the work is a 

 useful Glossary not found in the earlier editions ; but the 

 author has wisely refrained from acceding " to the wislies 

 of some young botanists by prefixing a short Introduction 

 to Botany." With the numerous admirable works now 

 at their disposal, students ought to have no difficulty in 

 making themselves acquainted with the Flora of the 

 British Islands. A. W. B. 



Eclipses, Past and Future, wi/h Cenei-al Hints for 

 observing the Heavens. By the Rev. S. J. Johnson, 

 M.A., F.R.A.S., Rector of Upton-Helions, Devon. 

 (Parker, 1S74). 

 This little book is a combination of two distinct treatises ; 

 one a description of past and future eclipses ; the other, 

 a catalogue of celestial objects falling within the range of 

 such small telescopes as amateurs frequently possess. 

 Each of these, it seems, was originally of greater bulk, 

 and intended for separate publication, but they have now 

 been condensed into a single small volume. This has the 

 merit, not very common in these days, of bemg more 

 than a mere compilation ; the ancient eclipses, including 

 those in the '' Saxon Chronicle '' (of which the author 

 tells us no description has hitherto been published), 

 having been approximately computed for the purpose 

 from the tables in the " Encyclopicdia Britannica;" and 

 the notices of the planets, double stars, &c., being derived 

 from actual observation. The book is pleasantly written, 

 and without professing to go deeply into the subject, may 

 well find readers among those who feel a general interest 

 in astronomy, but have no intention of making it matter 

 of serious or accurate study, or of going much beyond 

 the Imiits of a 2^- in. telescope. It would have been im- 

 proved ("without departing from its sketchy character) 

 by a little more fulness and explicitness of treatment in 

 some places ; for instance, in the description of the belts 

 and satellites of Jupiter, and where the abbreviated sym- 

 bols of the Palermo Catalogue are left unexpl.iinf d. Some 

 misprints, too, have escaped in the revision. The follow- 

 ing extract may interest our readers : — " For those who 

 have very large telescopes, and who are not disposed to 

 take them to oriental climates, it would be useful to have 

 records of the number of clear nights in different parts 

 of the kingdom. By clear nights, let us understand nights 

 cloudless, or nearly so, till 1 1 P.M., or else clear for a full 

 hour or two. Formerly my obsci-vations wtre taken in 

 South Lancashire, but since the early pait of 1870 in 

 Devonshire. In 1859, the number of nights clear, partly 

 or throughout, was 60 ; in i860, 43 ; in 186 1 and 1862, 

 46 each ; in 1863, 47 ; in 1S64, S3 ; m 1865, 82 ; in 1866, 

 77 ; in 1S67, 55 ; in 1868, 62 ; in 1869, 58 ; in 1870, 112 ; 

 in 1871, gS ; in 1S72, 90 ; in 1873, 82." 



The Human Eye. By W. Whalley. (London : J. & A. 

 Churchill.) 



In this small work the author tells us that he has incor- 

 porated the substance of a lecture on the subject, together 

 with additions in various directions. He discusses, in a 

 {.opular manner, the eye in man, and adds many facts 

 with regard to its structure in other animals. His remarks 

 are mostly anatomical, and we are disappointed to see so 

 little notice of many physiological phenomena connected 

 with the power of sight, which bring out the beauty of the 

 organ of vision in a way which can be understood by the 

 most amateur of readers. There is a want of consecutive- 

 ness in many of the paragraphs and chapters, though as 

 a whole the book is a very readable one. Many of the 

 instances given are wanting in gi asp ; for instance it is 



remarked that " In some of the ichneumons or ' Pharaoh's 

 rats,' as the Egyptians call them, in the coatimundi, which 

 somewhat resembles the racoon, and in the mangre, the 

 osseous orbital ring is incomplete, and in a group of minor 

 quadrupeds, entitled the Hyracida:, the malar, or cheek 

 bone, constitutes a perfect orbital ring." It is well known 

 that the orbital ring is complete in all the Quadiumana 

 and many Ungulata, and that it is absent inmost other 

 mammals ; why then take the particular examples, which 

 are not particularly good ones, and lay special stress on 

 them. The deductions drawn are of a strongly teleological 

 nature, and we cannot do better than recommend the 

 author's reperusal of his work for the refutation of one of 

 his concluding remarks, namely, that " In reviewing this 

 very imperfect and disconnected sketch of the structure 

 of the eyes of the different classes of animals, we cannot 

 fail to recognise the fact that the human eye far trans- 

 cends, both in mechanism and power, that of every other 

 animal." We however deduce that the condor can see 

 further, that many animals have an extra eyeUd, and 

 some bigger eyes than man himself, showing that his is 

 inferior instead of superior in many respects. 



LETTERS TO THE EDITOR 



[ The Edilor does not hold himself res fonsible for opinions expressed 

 by his correspondents. No notice is taken of anonymous 

 communications i\ 



Early Contributions to Spectrum Photography and 

 Photo-chemistry 



1. My first attempt at photographing the fixed lines of the 

 fpectium was made in 1834. It was on paper covered with silver 

 biomide. As mentioned in the Pliilosophical Magazine, May 

 1S43, it proved to be a failure. In the summer of 1S42, simul- 

 taneously with M. Becquerel, by using daguerreotype plates, I 

 succeeded, and in the following" March sent a drawing of the 

 photograph to the Pliilosophical Magazine, which was published 

 in May. At that time I did not know that M. Becquerel was 

 experimenting in the same direction. 



The great lines a, /3, 7, less refiangible than the rest, and 

 which M. Lamansky lias leccntly re-detected by the aid of the 

 Ihermo-multiplier, are given in that drawing. These in the 

 diffraction spectrum must be bands of very considerable width. 



2. Sometimes a jierson is deprived of fair credit for his labour 

 by what may be termed public perversity. I experienced this in 

 the case of llie chlorine and hydrogen photometer. The principle 

 of this instiument is, that chlorine and hydrogen obtained in 

 equal volumes by the electrolytic decomposition of hydrochloiic 

 acid, are made to reunite by exposure to light. I described a 

 simple instrument of the kind in the Philosophical Afagazine !oc 

 IJecember 1S43. It still remains the most sensitive fall photo-o 

 meters. Twelve jears subsequently, Professors Buns^n and 

 Koscoe modified it, and used it in their photo-chemical re- 

 searches. In their memoirs, published iir the Transactions uf 

 the Royal .Society, tliey give full credit for the invention to me, 

 and rennrk that by its use I had "succeeded in establishing 

 experinjentally some of tl-e most important relations of the 

 chemical action of light." They did justice in the matter, but 

 not so the public. The instrument currently passes as their 

 invention, not mine. 



While speaking of photometers there is ano'her to which I 

 may allude. It depends on the principle that a solution of ferric 

 oxalate is decomposed with evolution of carbonic acid on expo- 

 sure to light. The carbonic acid may be measured or weighed 

 by any ol the ordinary methods. I described such an instru- 

 ment ill the Pliilosophical Magazine, Sept. 1S57. Quite recent'y 

 M. Marchand has published in his Annates je Chcmie sevcial 

 experiments by its use, evideirtly unaware that it had been eni- 

 plojed by me many years ago. 



3. In 1S43 I made photographs of the diffraction spectrum 

 formed by a grating both by reflection ar d transmission, an! 

 published drawings of them. An account ol this may be seen 

 in the riiilosophicat Magazine June 1845 and March 1S57. These 

 were the first diffraction photographs ever made. They there- 

 fore preceded those of M. Mascart by many year's. Of course 

 they were not at all comparable with the very fine ones obtained 

 recently by my son. Dr. Henry Draper. 



