June 2 i, 1906] 



NA TURE 



175 



The note under criticism purports to be a " proof " that 

 the base originally used by Napier was the reciprocal of 

 c, and not e itself. In reality, it is nothing of the sort. 

 The arithmetical details are bolh unnecessary and in- 

 sufticient for the purpose, and their insertion is unfortu- 

 nately calculated to deceive many readers by obscuring the 

 real points at issue. The same " proof " might et|ually 

 well be employed to show that the original base was f 

 instead of its reciprocal, but that the minus sign had been 

 omitted from the logarithms of sines. If your correspon- 

 dent will read any treatise on the history of mathematics, 

 he will see an account of the train of reasoning which led 

 Napier to the discovery of logarilhms before the existence 

 of a base or the connection between logarithms and indices 

 had been suspected. There are doubtless many historical 

 points connected with the discovery of logarithms that 

 deserve closer study than they commonly receive, but the 

 publication of a book of this kind is not likely to advance 

 our knowledge of them. If one could be certain that all 

 readers would take the book for what it is worth, no 

 harm would be done. But there are, unfortunately, many 

 people who possess a " little knowledge " (which is, of 

 course, a " dangerous thing ") who will derive a large 

 amount of misinformation from the interpretation thev 

 will place on the contents of the book, and this misinform- 

 ation will be very difficult to eradicate. 



The Reviewer. 



Distribution of the Forms of Corvus comix and 

 C. corone. 



I SHOULD esteem it a favour if the writer of the review 

 of Ralfe's " Birds of the Isle of Man " (Nature, May 31, 

 p. 195) would more clearly explain his • reference to the 

 dimorphic forms of Corvus comix and C. corone, and the 

 " border-line, i.e. along the line from the Firth of Clyde 

 to the Adriatic, &c." 



The Firth of Clyde is not the limit of the line where 

 they are known to interbreed. They interbreed north of 

 the Firth of Forth, and as far north as Moray at least. 



And as regards the Adriatic, the forms are known to 

 interbreed and produce every variation of crosses or diverse 

 plumages in Siberia. 



No doubt your reviewer will be able to explain his 

 meaning, but, as at present expressed, it is somewhat 

 difficult to understand {v. p. 105). 



The " carrion crow " (corone) seems to me to be the 

 more aggressive of the two, and is slowly but surely push- 

 ing north in Britain, as I think references to our series of 

 Scottish faunas will show. 



J. A. Harvie-Brown. 



Dunipace, Larbert, Stirlingshire, N.B., June 2. 



The precise line — if there be one — marking the distribu- 

 tion between the breeding areas of Corvus comix and 

 C. corone is of little importance to the " problem " sug- 

 gested to the readers of N.^ture in the review mentioned. 

 Its direction, however, was taken from Newton's trust- 

 worthy " Dictionary of Birds," p. 117, where it is stated 

 to be " an irregular line drawn diagonally from about the 

 Firth of Clyde to the head of the Adriatic." The reviewer 

 cited that statement as authoritative, since he has had 

 no opportunity of personal observation on the subject. It 

 is further stated on the page last cited, '* it has now been 

 incontestably proved that along or near the boundary 

 where these two birds march, they not infrequently inter- 

 breed, and it is believed that the hybrids which sometimes 

 ■wholly resetnhle — italics by the reviewer — one or other of 

 the parents . . . pair indiscriminately among themselves or 

 with the pure stock." If these be established facts, then 

 the hybrid wholly resembling the black variety must, if it 

 occur in an\< considerable numbers, retire to breed " to 

 the south-western part of this quarter of the globe," and 

 the hybrid wholly resembling the " grey neck " " to the 

 north-eastern portion." How has this discrimination been 

 acquired? Two furtlier questions may be asked: Can the 

 wholly black and wholly grev hvbrids be recognised after 

 they have left the nest? Can the proportion of pure breeds 

 to hybrids in the general crow-population be determined? 



The facts given in Mr. Harvie-Brown 's letter seem to 



NO. T912, VOL. 74] 



indicate that the crows in their nursery arrangements 

 behave less perplexingly than the reviewer had deduced 

 from the statements he has quoted above. The black and 

 the grey crows may really be, therefore, not dimorphic 

 forms of one species, but two distinct species. 



TllK RlCVlEWER. 



The Date of Easter. 



In your issue of April 5 an enipirical formula is given 

 for determining the date on which Easter falls in any 

 year from 1900 to 2100. Having tried the formula for 

 certain years within the limits stated, I find that it fails 

 in the case of igS4- For that year it gives April 25, 

 whereas the correct date is April 18. Perhaps some of 

 your correspondents may be able to explain the cause of 

 the discrepancy. Alexander D. Ross. 



Glasgow, June 1. 



Your correspondent is correct in saying that the empirical 

 formula of Gauss for determining the date of Faster gives 

 April 25 for the year 1054, and I must confess my inability 

 to assign a reason for its failure in this particular instance. 



CllAS. I.KICII. 



The Victori:i L^nivrrsity of Manchester, June 12. 



Geological Survey of Canada. 



In the issue of Nature of April 26, under the heading 

 of " Notes," is a paragraph concerning changes in the 

 organisation of the Geological .Survey of Canada. This 

 paragraph is liable to be misleading, and I shall be greatly 

 obliged if you will kindly state the facts as they are. On 

 March 27 last Mr. A. P. Low was appointed deputy head 

 and director of the Geological Survey Department, and, at 

 the same time. Dr. R. Bell simply returned to his former 

 position of assistant-director and chief geologist, to which 

 he had been appointed in 1892. 



A. P. Low (Deputy Head and Director). 



Geological Survey of Canada, Ottawa, Ontario, May 29. 



THE FOSSIL VERTEBRATES OF THE 

 FAYUM.'^ 



A FEW years ago it was the fashion among 

 •'*- vertebrate pateontologists to sav that, at least 

 so far as the Tertiary period is concerned, the Old 

 World was played out in the matter of their speciaf 

 science, and that the scene of advance was shifted 

 to .A.merica, where alone important and epoch-making 

 discoveries were to be expected. All this has been 

 changed by the discovery of the wonderful Lower 

 Tertiary vertebrate fauna — or, rather, series of faunas 

 — in the Fayum, or lake-province, of Egypt, which 

 Dr. Andrews (who, we are glad to say, has now 

 the privilege of adding the letters F.R.S. to his 

 name) has so admirably and lucidly described in the 

 handsome quarto volume before us. Indeed, it is 

 not saying too much to assert that these discoveries 

 have practically revolutionised our conceptions of 

 the mutual relationships of several mammalian 

 groups, and also our ideas on many points connected 

 with the past distribution and migrations of the 

 mammals of the Old World. Perhaps the most im- 

 portant problem which Dr. Andrews has succeeded 

 in solving is the origin of the Proboscidea ; and if 

 this had been the only result of his labours he would 

 have been well entitled to undying fame. As it is, 

 this discovery is only one of several of the highest 

 importance in regard to mammalian evolution we 



1 "A Descriptive Catalogue of the Tertiary Vfrtebrata of the Fayflin, 

 Egypt; based on the Collection of the Eeyptian Government in the 

 Geological Museum, Cairo, and on the Collection in the British Museum 

 (Natural History), London." By C. W. Andrews. Pp. .\xxv:i-)-324 ;: 

 pis. 26, and text-figures. (London ; Printed by order of the Trustees 

 of the British Museum, 1906). Price 35.5. 



