Sept. 23, 1880] 



NATURE 



4S3 



gamic, that these subjects can no longer be treated oi pari 

 passu with the structural, if this latter is to be brought up 

 to the present state of knowledge in a work of the scope 

 and design of the authoi's " Text-Book." This has deter- 

 mined Dr. Gray to enlarge the scope of his work, to 

 retain the authorship of one volume, which is de- 

 voted to Morphology, Taxonomy, and Phytography, 

 re-writing these throughout, to assign another upon 

 Vegetable Histology and Physiology to his colleague. 

 Prof. Goodall; a third, which wall be an Introduction to 

 Cryptogamous Plants, to another colleague, Prof. Farlow ; 

 and to complete the series by a fourth, from his own pen, 

 on the Morphology and Classification of Flowering Plants, 

 their Distribution, Products, &c. 



Thus, when complete, we shall have from the most 

 eminent botanical professors in the New World as compre- 

 hensive an introduction to the study of the Vegetable King- 

 dom as the nineteenth century is likely to produce. 



OUR BOOK SHELF 

 Lis^ltt and Heat ; the Manifestations to our Senses of the 



Two Opposite Forces of Attraction and Repulsion in 



Nature. By Capt. W. Sedgwick, R.E. (London: 



Hodgson and Son, 1880,) 

 The reviewer who says what he thinks is sometimes 

 thought unkind. The author's paradoxes require no 

 commentary but themselves to be duly appraised by 

 scientific readers. 



" The explanation of the fact that a spot of light is 

 seen alike when pressure is applied to the outside of the 

 eye, and when a single ray of light passes into the eye, is 

 that the ray of light really makes itself manifest to our 

 sense of vision by exerting a pull upon the retina of the 

 eye ... it follows, of course, that light is a pulling or an 

 attractive force, and is therefore opposed to heat, which, 

 as is well known, is a pushing or repulsive force." 

 (Pp. 14 and 15.) 



" Light consists of a large amount of the attractive 

 force, mixed with a small amount of the repulsive force. 

 Heat, on the other hand, consists of a large amount of 

 the repulsive, with a small amount of the attractive 

 lorce." (P. 28.) 



"We have in the growth of plants and trees a beautiful 

 cxemphfication of the action of heat and light as expan- 

 sive and attractive forces. The young shoots are extended 

 by the expansive power of heat, and then the attractive 

 power of light comes into play" ... (P. 38.) 



" It may be objected that gravity cannot be the same 

 force as light, because, if it were, it would be greater by 

 day than by night." (P. 42.) 



" There is ample evidence all about us to testify to the 

 fact that light is an attractive force. Indeed we our- 

 selves bear witness to the fact by our fondness for fireworks 

 and illuminations" . . . (P. 38.) 



" Light being the manifestation, in the free state, to 

 our senses of the attractive or cohesive force . . . the 

 fact that the production of light is made the first act in 

 the creation of the world, in the account given us in the 

 Book of Genesis, becomes intelligible." (P. 42.) 



" I ask for no other favour, and for no mercy." (P. 3.) 



We believe we have sufficiently complied with the 

 gallant captain's request. S. P. T. 



The Land and Freshwater Shells of the British Isles. By 

 Richard Rimmer, F.L.S. (London: David Bogue, 

 1880.) 



This unpretending and well-written volume is dedicated 

 t3 the artisans, with many of whom, especially in the 

 Isorth of England, the subject is very popular. The 

 dedication is qualified, viz. : " To those of my country- 



men among the working classes who wisely employ their 

 leisure hours in the pursuit of useful and elevating know- 

 ledge, with the hope that others among their ranks may 

 be induced to forsake the paths of profitless and degrading 

 dissipation." William Edward, the Banff shoemaker, is 

 (thanks to Mr. Smiles) a celebrated example of the more 

 intelligent workman ; and we know of others who, how- 

 ever, "carent vato sacro." The book is very readable ; 

 it gives an excellent account of the habits of our land and 

 freshwater mollusks, as well as of their various habitats, and 

 it is not burdened with any synonymy or useless aliases. 

 It is founded on Dr. Gwyn Jeffreys' " British Conchology." 

 But the present work has a drawback. Eight out of the 

 eleven plates give photographs of the shells, which are 

 produced by the "Albertype" process; and the figures, 

 especially of the smaller species, are so blurred or 

 smudgy as to be almost undistinguishable. Plate X. is 

 very good, representing magnified views of the British 

 species of Vertigo. There is a useful glossary. 



LETTERS TO THE EDITOR 



\_Tlie Editor does not hold himself responsible for opinions expressed 

 by his corres/ondt nts. Neither can he undertake to return, or 

 to correspond with the writers of, rejected manuscripts. No' 

 notice is ta/ien of anonymous communications.'\ 



[ The Editor urgently requests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible otherwise to ensure the appearance even of coix- 

 munications containing interesting and noz'cl facts i\ 



Novel Celestial Object 



The search for planetary nebulje, described in Nature, 

 vol. xxii. p. 327, was continued for several evenings without 

 revealing any new object, although it is estimated that the 

 spectra of about loo.coo stars were examined. On the evening 

 of August 28 an object entered the field which presented a faint 

 continuous spectrum with a bright band near each end. Clouds 

 interfered and barely permitted an identification with Oeltzen- 

 17681, or a position in iS8oof R.A. iSh. im. 17s., Deo. - 21° 16'. 



This object might be mistaken for a temporary star like that 

 in Corona in 1863, and the bands assumed to correspond to the 

 hydrogen lines C and V . Tliis view is contravened by the 

 permanency of the object which was observed by Argelander in 

 1849, and at the Washington Observatory in 1S48 and 1849. 

 In all these cases its magnitude was estimated as 8, or very 

 nearly its present brightness. No variation of light was detected 

 between August 28 and September i. The star Oeltzen 17648 

 precedes it very nearly a minute, and is only four minutes north, 

 so that their light can be easily compared. As they are nearly- 

 equal, a slight change would be quickly recognised. 



A further examination of the spectrum showed that the less 

 refrangible band is near D, and the other between F and G. 

 The images of both, but particularly of the second, are much 

 elongated by the prism, showing that they are bands, and not 

 lines. The limits of wave-length of the first band are approxi- 

 mately 5,Soo and 5,850 ; those of the second, 4,670 and 4,730. 

 A band at 5,400 and some other fainter bands were also sus- 

 pected, but their existence is not certain. 



The discovery of this object greatly increases the difficulty of 

 distinguishing between a star and a planetary nebula. If the 

 disk is used as a test, the first object described in the paper re- 

 ferred to above might easily be taken for a star. If we define a 

 nebula by its spectrum of bright lines on a faint continuous 

 spectrum, the object now under consideration becomes a nebula. 

 Whether it is a mass of incandescent gas resembling a nebula in 

 character, but not in constitution, or whether it is a star h iUi a. 

 vast atmosphere of incandescent gas of a material not as yet 

 known to us, are questions which cannot yet be decided. 



Cambridge, U.S., September 2 Edw.\rd C. Pickering. 



Experiments on the States of Matter 

 The exploration of the new region which I have lately opened 

 up has led to so many results with both scientific and technicai 

 bearings that I have been unable to leave this city for some time 

 to attend any scientific meetings, and I would beg leave, with 

 your kind permi;sion, to n.ake, tlu-ough the medium of your 

 valuable columns, a few remarks ou some recent scientific work. 



