February 23, 1893] 



NATURE 



389 



philosophy and science. Mr, Steele has done his work 

 with much tact and care, and an interesting preface is 

 contributed by Mr. William Morris. 



Astronomy for Every-day Readers. By B. J. Hopkins, 



F.R.A.S. (London : George Philip and Son, 1893.) 

 This is a little book which aims at explaining in " as 

 accurate and interesting a manner as possible such of the 

 phenomena of the heavens as should be known to every 

 intelligent person." It consists of six chapters dealing 

 respectively with day and night, the phases of the moon, 

 the tides, the seasons, eclipses, meteors, shooting stars, 

 and comets. Descriptive astronomy is not touched upon, 

 but there is an introductory chapter giving a general 

 survey of the solar system and its dimensions. The book 

 has been very carefully written, and the scientific ex- 

 planations are much relieved by interesting references to 

 the history of the subject. The author has succeeded in 

 giving very clear and concise accounts of the every-day 

 phenomena with which the book specially deals, and it 

 seems well adapted to awaken a desire for more in the 

 class of readers to whom he more particularly appeals. 

 A biography of the author — who is described as "the 

 working-man scientist '' — is also included. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers o/, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. "[ 



Blind Animals in Caves. 



In an article in the current number of the Contemporary 

 Review Mr. Herbsrt Spencer discusses the "familiar instance" 

 of blind animals in caves as bearing upon the hypothesis of 

 the transmission of acquired characters. Mr. Spencer is not 

 satisfied with the explanation of the blindness of these cave 

 animals offered by Weismann, who endeavours to account for 

 them by two conditions recognised as operating in regard to 

 other cases by Darwin, viz. cessation of selection and 

 parsimony of growth ("Origin of Species," sixth edition, 

 p. 118), of which the former author has treated under 

 the name Panmyxia. Mr. Spencer shows that the saving of 

 ponderable material in the suppression of an eye is but a small 

 economy: he loses si-ht of the fact, however, that possibly, or 

 even probably, the savmg to the organism in the reduction of an 

 eye to a rudimentary state is not to be measured by mere bulk, 

 but by the non-expenditure of special materials and special 

 activities which are concerned in the production of an organ so 

 peculiar and elaborate as is the vertebrate eye. 



That, however, to w hich I wish here to draw the attention of Mr. 

 Spencer and his readers is this : — Mr. Spencer appears to think 

 that if he disposes of Weismann's explanation of the blindness 

 of cave-animals according to "Panmyxia" — there remains 

 only the explanation by "transmission of acquired characters" 

 in the field. He appears not to be acquainted with the explana- 

 tion which I have offered of the blindness of cave-animals. It 

 is closely similar to that given by Darwin of the occurrence of 

 wingless insects on oceanic islands. My explanation consists in 

 an application to the case in hand of Darwin's principle of 

 " natural selection," I published it some years ago in my article 

 "Zoology" in the " Encycl. Britannica," reprinted in 1890 in a 

 volume of essays, bearing the title " The Advancement of 

 Science." My suggestion was (and is) as follows, and I should 

 like to see what Mr. Spencer has to say to it : — " This instance 

 (that of the blind cave-animals) can," I wrote in the article above- 

 named, " be fully explained by natural selection acting on con- 

 genital fortuitous variations. Many animals are thus born with 

 distorted or defective eyes whose parents have not had their 

 eyes submitted to any peculiar conditions. Supposing a number 

 of some species of Arthropod or Fish to be swept into a cavern 

 or to be carried from less to greater depths in the sea, those in- 

 dividuals with perfect eyes would follow the glimmer of light 

 and eventually escape to the outer air or the shallower depths, 

 leaving behind those with imperfect eyes to breed in the dark 



NO. 1217, VOL. 47] 



place. A natural selection would thus be effected. In every 

 succeeding generation (bred in the dark place) this would be 

 the case, and even those with weak but still seeing eyes would 

 in the course of time escape, until only a pure race of eyeless or 

 blind animals would be left in the cavern or deep sea." 



My own position in regard to the hypothesis of the transmis- 

 sion of acquired characters remains what it was ten years ago, 

 viz. that in the absence of observed instances of this transmission 

 and in the presence of repeated observation that particular 

 acquired characters are not transmitted, I do not consider it 

 legitimate to assume a transmission of acquired characters as the 

 explanation of any given case, such, for instance, as that of the 

 blind cave-animals. I am confirmed in this attitude by the fact 

 that a little consideration has enabled me and others to explain 

 satisfactorily, by reference to no hypothetical causes, but to the 

 admitted and demonstrable facts of "congenital variation" 

 and "natural selection," instances brought forward as "only 

 to be explained on the assumption of the truth of Lamarck's 

 hypothesis." 



On the other hand, I have always considered that there is not 

 sufficient ground for asserting that a transmission of acquired 

 characters can not take place. The important question is still as 

 it was five years ago, "Does it take place?" 



Oxford, February 14. E. Ray Lankester. 



Glacier Action, 



I have read with great interest and pleasure the short review 

 in your paper of last week by Prof. Bonney, giving a summary 

 of the results of a survey of the French freshwater lakes, and in- 

 dicating as the most probable conclusion that they cannot be 

 accounted for on the theory of the late Sir A. Ramsay, by the 

 digging-out power of glaciers. 



Living as I do in a highly glaciated country, and in a country 

 also full of lakes, both fresh and salt, I have never believed in 

 that theory. Lakes seem to me to be due to the same causes 

 which have produced the glens and hollows in which they lie, 

 and these causes cannot be identified with glacier action alone. 

 The theory of Ramsay attributes to glacier action powers and 

 effects which have never been proved to belong to them. 

 Glaciers do not dig out. They rub down — abrade — and scoop, 

 when they are moving down inclined planes at angles more or 

 less steep. But when they reach level ground they do not dig ; 

 they rest upon the level surfaces, and when pressed from behind 

 they flow over it. But I have never seen any proof that they 

 can act like a ploughshare, or rather like one of the new digging 

 machines. 



In so far as all existing glens may have been formerly occupied 

 by glaciers, their depths must have been increased by glacier 

 action, on the supposition that they were tilted, or upraised at 

 some angle required for this form of true glacier action. On this 

 supposition, indeed, lake basins may be said to be partly due to 

 glaciers. But then this supposition involves and depends upon 

 the assumption that earth movements have made the lake basins 

 what they now are — hollows in a comparative level. 



Like all other general theories in the history of geology, the 

 "glacial theory" seems to me to have been ridden to the death, 

 and I have been long wailing for some signs of that reaction or 

 correction which is still much needed. I hold that in this country 

 there is not only no evidence of " ice sheets " overriding all the 

 hills, but the strongest evidence against such sheets. Our glens 

 had true glaciers in abundance, no doubt, and they have 

 left their tool-marks very distinctly. But those marks are quite 

 inconsistent with one universal ice-cap or ice-sheet over all the 

 land. Argyll. 



Inveraray, February 16. 



Dr. Joule's Thermometers. 



Every one will, I am sure, be glad to know that Dr. Joule's 

 thermometers are under investigation by Prof. Schuster. 



It is unfortunate that Joule does not give the actual readings 

 of the freezing point, but if the comparison quoted by 

 Rowland was made in either 1879 or 1890 it may be that he 

 referred to the reading of November, 1879, when the total rise 

 of the zero point was 12-92 scale divisions. In that case the 

 original reading in April, 1844, would be 970 ; at any rate this 

 number cannot be very far from the truth. 



The temporary changes of zero point alluded to by Prof. 

 Schuster certainly complicate the matter, but from the numbers 

 given it would appear that since 1879 or 1880 there has been a 



