Nov. 



I87IJ 



NATURE 



59 



discreetly made between certain supposed species, of 

 which he has examined a large series of specimens in 

 a most exhaustive and painstaking manner. 



In Part V. of his memoir Mr. Allen treats of the 

 geographical distribution of the birds of North America, 

 " with special reference to the number and circumscription 

 of the ornithological faunas." In this essay, which well 

 merits perusal, although it is evident that the author has 

 never made himself acquainted with some of the most 

 certainly ascertained facts of the general distribution of 

 bird-life,* a new and arbitrary division of the world's 

 surface into eight "realms " is proposed. 



The division of North America, however, into its con- 

 stituent sub fauna: is fully discussed and well worked out. 

 An appendix to the volume contains a list of authorities 

 to be consulted on the geographical distribution of North 

 American birds, which will be useful, although by no 

 means well arranged. Mr. Allen's knowledge of the 

 geography of Central America seems, moreover, to be 

 somevvhat imperfect, as Mr. Salvin's articles on the birds of 

 Veragua are placed under " Guatemala," and papers 

 relating to British Honduras [i.e., Belize), the Republic of 

 Honduras, and Nicaragua, are all confounded under one 

 head. P. L. S. 



OUR BOOK SHELF 



Sir Isaac Newton's Principia. Reprinted for Sir W. 

 Thomson, LL.D., and Hugh Blackburn, M.A. (Glas- 

 gow : Maclehose.) 

 Finding that all editions of the Principia are out of print, 

 the Glasgow Professors of Natural Philosophy and of 

 Mathematics have issued a careful reprint of the last 

 (third) edition as finally revised by Newton himself; at- 

 tending, of course, to the Corrigenda, but wisely abstain- 

 ing from the insertion of either note or comment. We 

 have had far too much of such things. Thmk only of the 

 painfully elaborate notes of poor Bishop Horsley, which 

 deface an otherwise splendid edition, and of the truly 

 amazing comments made by Lord Brougham in his "Ana- 

 lytical Views !" True, these are coarse attempts at paint- 

 ing, or rather at "whitewashing," while the Glasgow 

 professors are quite able to " gild." But even gilding 

 would have had a smack of profanation about it, and we 

 are delighted to have Newton left to speak for himself in 

 the old, imperishable, words whose full meaning is only 

 now gradually dawning on the world. So far as we have 

 compared it with other copies, this edition seems to be 

 better than any of its predecessors ; the printing and 

 paper are excellent, and the cuts especially are greatly 

 improved. There is, however, one remark which is (orcibly 

 thrust upon us by this performance. How eccentric and 

 inscrutable are mathematicians ! Comets are nothing to 

 them ; and the greater they are, the less do they seem 

 subject to any law of what would be called common sense 

 by mere average humanity. One man of exceptional 

 genius is found wasting day after day in neatly rounding 

 off a sonnet ; anon he calculates, to fifty places more than 

 can ever be required, the root of some transcendental 

 equation. Others occasionally burst from their seclusion 

 and rush wildly into gymnastic feats, high-jinks, and what 

 not ; but in cold blood to determme to verify, letter by 

 letter, a reprint of a somewhat bulky Latin book seems a 

 species of self-torture, of which nothing we ever before 

 heard concerning our northern friends, could have led us 



* E.g. The "Neotropical Region" of Sclater, i.e.. South and Central 

 America, is divided between two "realms," an " American Tropical " and 

 a " South -American Temperate," than which nothing can be more unnatural, 

 and North America is parcelled out into " three realms !" ^ ._^ 



to imagine them capable. They have gone through it, 

 however; and, having done it well, deserve our hearty 

 thanks. 



Description of an Electrical Telegraph. By Sir Francis 



Ronalds, F.R.S. (London : Williams and Norgate ) 

 Sir Francis Ronalds has done well in republishing this 

 portion of his work, which was first printed in 1823. The 

 hope which he expresses in the preface to this reprint that 

 his name "may remain connected with an invention 

 which has conferred incalculable benefits on mankind," 

 is quite justified by the experiments which he made and 

 published many years before the final success of tele- 

 graphy. Sir Francis, before 1823, sent intelligible mes- 

 sages through more than eight miles of wire insulated 

 and suspended in the air. His elementary signal was 

 the divergence of the pith balls of a Canton's electro- 

 meter produced by the communication of a statical 

 charge to the wire. He used synchronous rotation of 

 lettered dials at each end of the line, and charged the 

 wire at the sending-end whenever the letter to be indi- 

 cated passed an opening provided in a cover ; the elec- 

 trometer at the far end then diverged, and thus informed 

 the receiver of the message which letter was designated by 

 the sender. The dials never stopped, and any slight 

 want of synchronism was corrected by moving the cover. 

 Hughes' printing instrument is the fully developed form of 

 this rudimentary instrument. A gas pistol was used to draw 

 attention, just as now a bell is rung. The primary idea 

 of reverse currents is to be found where Sir Francis sug- 

 gests that the wire when charged with positive electricity 

 should discharge not to earth but into a battery nega- 

 tively charged. Equally interesting is the discussion on 

 what we now call lateral induction, then known as com- 

 pensation. The author clearly saw that in the under- 

 ground wires which he suggests as substitutes for aerial 

 lines, this induction would be or might be a cause of re- 

 tardation. His own words must here be quoted : — " That 

 objection which has seemed to most of those with whom 

 I have conversed on the subject the least obvious, ap- 

 pears to me the most important, therefore I begin with 

 it, viz., the probability that the electrical compensation, 

 which would take place in a wire enclosed in glass tubes 

 of many miles in length (the wire acting, as it were, like 

 the interior coating of a battery) iniglit amount to the 

 retention of a charge, or, at least, might destroy the sud- 

 denness of a discharge, or, in other words, it might 

 arrive at such a degree as to retain the charge with more 

 or less force, even although the wire were brought into 

 contact with the earth." This passage, written in 1823, is 

 very remarkable, and would alone entitle the author to 

 be mentioned in any history of underground or submarine 

 telegraphs. Testing-boxes were invented by Sir Francis, 

 and a code is suggested by him. If these things had 

 been mere suggestions they would have been remarkable, 

 but accompanied by practical experiments proving that 

 the scheme could be carried out, they ought to connect 

 his name permanently with the history of the Electric 

 Telegraph. F. J. 



LETTERS TO THE EDITOR 



\^Tlie Editor does not Iiold himself responsible for opinions expressed 

 by Ids correspondents. No notice is taien of anonymous 

 communications. ] 



Oceanic Circulation 

 On returning from my second Mediterranean cruise, I find 

 that Mr. CroU has published in the Phdosophical Magazine his 

 promised demonstration of the theoretical impossibility of the 

 production of under-currents by giavitation, according to the doc- 

 trine which I have advocated with reference to — 



1. The Gibraltar Current. 



2. The Baltic and Black Sea Currents. 



3. The General Oceanic Circulation. 



At the same time I find awaiting me a very important treatise 



