No\-EMBEB 1, 1897.] 



KNOWLEDGE. 



261 



however, is not altogether certain, and irradiation may | 

 here have played a very important part. ^ j 



In conclusion, vre believe that nothing can be alBrmed 

 regarding the rotation of Venus, inasmuch as the absorp- ! 

 tion of its immense atmosphere certainly prevents any 

 detail on its surface from being perceived. The most 

 careful discussion of all the observations leads us to think 

 that the grey spots now and again seen upon Venus are 

 the effects of contrast due to solar illumination, and that 

 the less definite shadings are of an atmospheric nature, 

 incapable of furnishing us with any serious data as to the 

 rotation of the planet. We may state here more than ever 

 that every man sees after his own fashion and draws after 

 his own fashion. We are siue of nothing. The globe of 

 Venus may turn underneath its opaque envelope without 

 any motion manifesting itself to our eyes — unless by some 

 transitory and uncertain effects. No one has ever seen on 

 the surface of Venus any clearly characteristic spot analo- 

 gous to those shown on the discs of Mars and the moon. 

 The maps of Venus made up to the present time are 



illusions. 



.^ 



BOOKS KECEIVED. 



Natural Causes and Supernatural Seemini/s. By Henry Maudsley, 

 M.D. Third Edition. (Kegau Paul.) 12s. 



The Centuries : a Chronological St/nopsis of Ristori) on the 

 " Space-for-Time " Method. Second Edition. (West, Newman, & Co.) 



The atory of Germ Life. By H. W. Conn. (Newnes.) Illus- 

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Lumen. By Camiile Flammarion. (Heinemann.) 3s. 6d. 



Tlte Machinerii of the Universe. By A. E. Dolbear. (Society for 

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Memory and its Cultivation. By F. W. Edridge-Grreen. (Kegan 

 Paul.) Illustrated. 5$. 



A Question of the Land and Water. By Dante Alighieri. (David 

 Nutt.) 28. 



The Mathematical Psychology of Gratz and Boole. By Mary 

 Ererest Boole. (Sonnenschein.) As. 



The Building of the Intellect. By Douglas iX. Gane. (Elliot 

 Stock). 53. 



Recent and Coming Eclipses. By Sir Norman Lockyer. (Mac- 

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Electricity in the Service of Man. By Dr. Wormell. Revised 

 and Enlarged by Prof. Walmsley. (Cassell & Co.) Illustrated, "s. 6d. 



The Works of Archimedes. By Dr. T. L. Heath. (Cambridge 

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Thermo-Geographical Studies. By C. L. Madsen. (Copenhagen : 

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The Dynamics of Religion. By M. W. Wiseman. (The University 

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Ornamental Design for Woeen Fabrics. By C. Stephenson and 

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The Elements of Astronomy. By Prof. Young. (Green & Co.) 

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Applied Mechanics. By Prof. Perrv. (Cassell & Co.) Illustrated. 

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Organic Chemical Manipulation. By J. T. Hewitt. (Whiltaker 

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John Hunter. By Stephen Paget. (Cnwin.) Portrait. 3s. 6d. 



A History of China from the Earliest Days down to the Present- 

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Humanitarian Essays. Various Authors. Edited by Henry S. 

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Practical Physiology. By Albert F. Blaisdell. (Ginn & Co.) 

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Montaigne and Shakespeare. By John M. Robertson. (The 

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Progress in Printing and the Graphic Arts during the Victorian 

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Sir George Xewnes, Limited, by special arrangement with Messrs. 

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PHOTOGRAPH OF THE MOON. 



A>je,9J.10h. 7m. 

 {See Collotype Plate.) 



THE accompanying photograph has an interest 

 beyond that attaching to it as a representation 

 of the moon, in that it was taken with a refractor 

 . ordinarily corrected for the visual rays, but which, 

 according to the plan suggested by Sir G. G. 

 Stokes, has been adapted for photography by reversing the 

 crown lens, and moving it somewhat further away from 

 the flmt lens. The delicacy of the detail shown in the 

 negative is a sufficient proof how thoroughly successful 

 the arrangement has been ; and as the importance of 

 photography is constantly on the increase in astronomy, 

 it points out an easy way of rendering an instrument 

 suitable at once for direct visual use, and for employment 

 with the sensitive use. There are several other methods 

 of securing the same result — the new triple achromatic 

 object glassies, designed by Mr. Dennis Taylor ; the addition 

 of a correcting lens to an ordinary achromatic, as in the 

 case of the thirty-six-inch refractor of the Lick Observa- 

 tory ; and in the employment of ortho-chromatic plates. 

 It should, however, be remembered that no objective has 

 yet been constructed on Mr. Dennis Taylor's principle 

 nearly so large as the twenty-eight-inch refractor of the 

 Royal Observatory, Greenwich, the telescope with which 

 the original of our plate was taken ; and that the aperture 

 of the Lick object glass is usually cut down to one-fourth 

 of its full diameter when used for lunar photography, 

 whereas the full twenty-eight inches were employed in the 

 Greenwich instrument. 



The plate used was a Hill-Norris dry collodion plate, 

 ea^le brand, with an exposure of half a second ; and it 

 wa°s taken on March 12tb, 1897, at lOh. 3m. G.M.T., by 

 Mr. T. Lewis, F.E.A.S. The plate was exposed m the 

 primary focus, the original having been enlarged three 

 diameters in the present reproduction, permission to make 

 which was kindly granted by the Astronomer Royal. 

 ♦ 



flrmrs. 



[The Editors do not hold themselves responsible for the opinions or 

 statements of correspondents.] 



•' MORE ABOUT ANTITENENE." 

 To the Editors of Knowledge. 



Sirs, — In continuation of the correspondence which has 

 arisen between Dr. McPherson and myself on the subject 

 of snake poison, I would point out that the wording of the 

 original statement in the article " More about Antiveuene," 

 which appeared in the September Number of Knowledge, 

 is as follows :— " Venom is almost inert when introduced 

 into the stomach. . . . After repeated experiments on 

 white rats, he (Prof. Eraser) found that when the snake's 

 poison is introduced mto the stomach it does not produce 

 any active poisoning effects, but some of it seems to be 

 absorbed into the animal's blood so as to assist in the 

 immunization. Why was this ? In Prof. Eraser's opinion, 

 when venom is introduced into the stomach, the chemical 

 changes wrought by the acids of the stomach destroy its 

 fatality to a large extent." 



The natural interpretation of this statement appears to 

 me to be that snake poison is harmless when introduced 

 into the stomach, and that this harmlessness is, to a large 

 extent, attributable to the action of the acids in the 

 stomach ; not, as Dr. McPherson explains in his reply to 

 my letter in the October Number of your paper, that snake 

 poison can be introduced into the stomach »// tu a certain 

 extent without producing any active poisonous effects. I 



