NA TL T RE 



[November 2, 1905 



A large part of the difficulty arises from the different 

 pi in < i view taken by the electrician and the physio- 

 logist respectively, the electrician being concerned chiefly 

 surfaces of conductors, the physiologist being 

 interested chiefly in the interiors of living tissues. 



Thus the above expression, " region A," is electrically 

 ambiguous, for it may mean (i) either the surface of the 

 1, or !-•) the interior of the same: certainly physio- 

 logically (and it may be also electrically) these are two 

 very different things. 



Are we speaking of surfaces or interiors when we talk 

 of tissues and their electromotive states? This seems to 

 me the gist of the initial obscurity. 



In Dr. Waller's terminology a is " zincative " to b; but 

 the electrically-minded student wishes to distribute his 

 + and — somehow. The electrician says a is " negative " 

 to B, because he is thinking of the surface at A to 

 which current has been coming from b, as he finds 

 by ihi- galvanometer; but the physiologist, conceiving of 

 what is going on inside the excited portion of tissue A, says, 

 or should say, "a is electropositive to B," because he 

 finds that current in the tissue must have come from a 

 to B. The ambiguity is bound up with not distinguishing 

 tin- surface from the interior. 



All doubt, it seems to me, is removed when wo say, 

 the region A is, as to its interior, electropositive to b, but 

 as to its surface electronegative to B ; as to its interior, i 

 is a " positive plate," as to its surface a " negative pole." 

 Both these ideas are necessarily connoted by "zincative," 

 only implicitly, however; for teaching purposes they must 

 be made also explicit. 



" Negativity of action " is then intelligible whin ii is 

 distinctly laid down that it is only the surface of tin- active 

 region that is being considered, for if the interior of the 

 active tissue is thought of, then positivity of action must 

 be the term descriptive of the electrical state. 



If, then, the qualifying term '* internally " or 

 "externally," as the case requires, be added, no loophole 

 for confusion is left; thus, A is internally electropositive 

 to b, externally electronegative to B; b is internally 

 electronegative tn a, externally electropositive to a; for 

 "externally," " galvanometrically " may bo used. 



Personally I think the use of the term " negativity of 

 action" is, especially if used in teaching, objectionable, 

 because misleading and mysterious; "internal positivity 

 of action" certainly seems to describe a real state; as 

 terms, the one is but the converse of the other. I have. 

 however, no more sympathy with those people who persist 

 in finding " negativity of action " entirely meaningless than 

 I have with those who will not understand "negative 

 pressure " or negative quantities of any kind. 



David Eraser Harris. 



Physiological Department, University, St. Andrews, 

 October 31. 



The Engineer's Unit of Force. 



In a review of some recent works on mechanics in your 

 issue of October 19, thi reviewer calls to account two of 

 the authors whose books are reviewed for " implying that 

 the unit of force in the engineer's system is a variable 

 quantity." 



Perhaps there may be others than the authors referred 

 to and myself who would welcome more explicit enlighten- 

 ment on the subject of the constancy of the engineer's 

 unit of force. ' D. J. Carnegie. 



October 23. 



The engineer's unit of force is equal to the earth's 



1" I'' attraction on the standard pound mass at a specified 



place, viz., for this country. London. In magnitude is 

 such that it produces unit acceleration when acting on a 

 mass of 32182 . . lb., the engineer's unit of mass, 

 sometimes 1 ailed a slugg (sluggish). The formula 

 M=W/g, where M is the mass in sluggs, is true for anv 

 latitude, g being the acceleration of gravity there, and W 

 the weight of the mass in pounds force, as would, for 

 instance, be registered at the place by a massless spring 

 balance which had been graduated in London. If the 

 pound-poundal system of units is an absolute dynamical 

 one, so also is the pound-slugg or engineer's system. 



The Reviewer. 



NO. l8/9, VOL. J$] 



PROF. LANKESTER'S "EXTINCT ANIMALS." 1 



THOSE who, like the writer, had the good fortune 

 ■*• to be present at the Royal Institution last 

 Christmas and listened to Prof. Lankester's course of 

 holiday lectures to young people will recall the fact 

 that, although a goodly space was occupied by boys 

 and girls from school, the theatre was elsewhere 

 crammed with "grown-ups," who were quite as 

 much interested and amused as the juvenile audience 

 for whom these discourses were really designed. 



It is, in fact, an open secret that quite elderly 

 young people, as much as schoolboys and girls, enjoy 

 their " ologies " when given to them in a form easy 

 of digestion and with as few hard words as possible. 



Before the memory of those pleasant afternoon dis- 

 courses has faded from our minds comes a reprint of 

 tin 111 in book form, with reproductions of more than 

 200 of the illustrations given in the text as we saw 

 them on the screen. 



Every boy and girl who heard those lectures will 

 wisli fur a copy of this charming book, and those 

 who did not will now read with delight the pictured 

 story of extinct animals for themselves; nor will the 

 " old boys " fail to take it up also. 



Prof. Lankestcr explains that extinct animals tire 

 tin ini- which no longer exist in a living state. 

 Animals, of course, die daily, and men too, but the 

 lecturer tells us of extinct kinds of animals which no 

 longer exist on the surface of the globe in a living 

 state, although once they flourished and held their 

 own. 



He then informs his young friends of his own 

 eail\- experiences as a boy in visiting the British 

 Museum and being fascinated by the huge head of 

 an Ichthyosaurus from Lyme Regis with its large 

 and bony-plated eyes, and its jaws, more than 3 feet 

 in length, armed with powerful teeth. 



Then the huge ground-sloth from South America 

 attracted his wonder and admiration by its vast bulk, 

 and he learnt that living' upon the leaves of trees, 

 but being too heavy to climb, it stood on the ground 

 and pulled the trees down to it in order to feed on 

 the j ig branches. 



Their remains, often with the bones of the same 

 individual lying in one spot, occur in the vast 

 " pampas formation " and in the alluvial mud of the 

 greal rivers such as the La Plata. Here, too, one 

 meets with the giant armadillo, and another strange 

 creature, called the Toxodon, like a huge guinea-pig, 

 nearly as big' as a rhinoceros, with tremendous chisel- 

 like teeth in front. 



Prof. Lankester shows the thigh-bone of a giant 

 reptile from North America more than 6 feet long 

 (known as Atlantosaurus). What the size oi the 

 entire animal must have been we can best judg"e by 

 paying a visit to the Cromwell Road Museum to see 

 the skeleton of the Diplodocus lately set up there, 

 which is 80 feet long and fully 14 feet high ! 



Passing rapidly over such forms as the ancient 

 rhinoceros, the northern hippopotamus, tin braver, 

 and great auk — once common in Britain, but now 

 extinct- the author tells how zebras, quaggas, 

 antelopes, and garaffes are being fasl killed off in 

 Africa by our sportsmen, whilst the dodo and 

 " Steller's sea-cow " were eaten up long ago, like 

 the giant tortoises, by our early voyagers, who 

 victualled their -ships, with these rare animals. 



The author next explains the causes which have 

 brought aboul the migration of some animals and the 

 extinction of others, and how changes of climate and 



1 "Extinct Animals." By E Ray ta 

 Pp. xxiv+3 3 a ; with 218 illustrations. (Lo 

 Co., Ltd., 1905 ) Price ^s. 6d. ne: 



