360 



♦ KNO^VLEDGE ♦ 



[Dec. 14, 1883. 



of the day, has had experience, in lecturing, of the require- 

 ments of the general public, not necessarily less instructed 

 all round than those who undertake to teach, but needing 

 clear and simple information, free from technical details, 

 respecting the leading truths of special branches of science, 

 with which the teacher has made himself familiar. 

 There is no greater mistake, we are convinced, than 

 is made by those lecturers and writers who regard 

 their audiences or readers as ignorant persons to be 

 addressed in condescending tone and with childish words. 

 Clearness and simplicity are all that the teacher needs to 

 go straight to the understanding of his audience. Ex- 

 pressed clearly and simply the grandest truths of science 

 while they lose nothing of their impressiveness become 

 acceptable to every reasoning being — a term which does 

 not include those who are so enamoured of a special sub- 

 ject as to have no room in their minds for other matters. 



Mr. Carpenter's subject is " Energy in Nature " in all 

 its varied manifestations, — as Heat and as Mechanical 

 Energy, as Light, as Magnetism, as Animal and Vegetable 

 Energy, as Gravitation, as Cohesion or as Radiant 

 Energy. 



In the first lecture our author discusses matter and 

 motion, force and energy. In this lecture a very clear and 

 succinct account is given of the laws of motion ; but we 

 must take some exception to the remark that " although a 

 body may be apparently at rest, it may have a very decided 

 tendency to move," as likely to be misapprehended. A 

 condition of readiness to respond to any application of 

 force can hardly be called a tendency to move. The case 

 cited by Mr. Carpenter, of two weights carefully balanced 

 and then moved with a slight addition to either, indicates 

 no tendency to move : the velocity acquired by the total 

 moving mass at the end of any given time is precisely that 

 resulting from the downward tendency of the added mass, 

 applied to the total mass moved, less such effect of fric- 

 tional resistance as may be excited during the motion. If 

 the small moving weight may be neglected as com- 

 pared with the large balanced weight, then when these 

 are doubled, trebled, quadrupled, &c., the resulting velocity 

 is reduced to one-half, one-third, one-fourth. A weight of 

 2 lb. hung by a long fine thread begins to move more readily 

 under slight side pressure than two balanced weights of 

 1 lb. each, — but because it is freer to move, not because of 

 greater or less tendency to move. This, however, is but a 

 slight defect in a very interesting chapter. The chapter 

 on Heat gives a very complete and interesting account of 

 all the principal facts to be noted in connection with heat 

 regarded as a form of energy. Here again we pass over all 

 the excellent descriptions and explanations, to touch on a 

 passage which seems likely to mislead, ^with no unfairness 

 however of intention, but rather dwelling on the fact that 

 the point seems the only one which needs correction ; the 

 rest of the chapter can take care of itself. Mr. Carpenter 

 says that radiant heat and light are not identical though 

 propagated in the same way : the waves which affect 

 the sense of touch as heat are much longer than 

 those which affect the eye as light. This, of course, 

 is not strictly correct. There are rays which 

 affect the sense of touch as heat and affect the sense of 

 sight as Ught. To such rays glass which is opaque to 

 obscure heat rays is as we know not opaque ; while iodine 

 in solution, which is absolutely opaque to light, is as abso- 

 lutely opaque to heat waves of this kind. The more correct 

 way of putting the matter would have been to say that 

 waves between certain limits of length affect the sense of 

 sight as light ; and that while the shorter of these waves 

 do not affect the sense of touch as heat the longer ones do, 

 while longer waves still, though not affecting the sense of 



sight, affect the sense of touch as heat in a still more 

 marked degree than even the longer light. 



We note also by the way that the statement at the foot 

 of p. 42, to the effect that " there is good reason for 

 believing that oceanic circulation is due rather to polar 

 cold than to equatorial heat " seems open to serious 

 question. To us it seems like saying that the processes 

 attributed to the sun's heat are really due to the cold 

 following his absence from the sky. 



The chapters on Chemical Attraction (including combus- 

 tion). Electricity and Chemical Action, and Magnetism and 

 Electricity are full of interesting matter. But the most 

 interesting and valuable chapter of all is, in our judgment, 

 the sixth, on Energy in Organic Nature. The comparison 

 between the animal body as a machine (p. 189) and the 

 very best forms of steam-engines as earlier described at 

 p. .54 is worthy of the most careful study. The discussion 

 of the value of various forms of food, though necessarily 

 brief, is excellent. We may say of this chapter that while 

 not one man in a thousand can afford to be ignorant of the 

 facts here dealt with, we doubt whether they are really 

 known to one in a million. 



THE WAYS OF SOME INDIAN INSECTS, 

 BEASTS, AND BIRDS.* 



This is a delightful book, irresistibly funny in descrip- 

 tion and illustration, but full of genuine science too. 

 The fun which E. H. A. finds in the ways of insects, beasts, 

 and birds belongs in truth to the poetry of this part of 

 science, as certainly as the solemn mystery of the star- 

 depths belongs to the poetry of astronomy. And as the 

 fun of our author is full of poetry so does it verge now 

 and then on the terrible or the pathetic. How humorously 

 he describes the microphonic ears and the distant-smelling 

 nasal appendages of the demon bat ; but we are more dis- 

 posed to shiver than to smile when he goes on to show how 

 this deadly creature hears and scents its prey. " Those 

 ears are fit to catch the gentlest rustle of the feathers of a 

 dreaming sparrow," its nasal trumpets "gather the faintest 

 odour of the sleeping prey as the demon bat floats past 

 upon the air." " It scents a sparrow asleep with its head 

 cosily buried in its wing. The sparrow has a dream, a 

 dreadful dream ; it starts and raises it head and gives a 



piercing shriek and the cui'tain falls In the morning 



two wings are lying beside the flower-vase upon the table, 

 and perhaps a beak, though the demon bat eats head, 

 skull and all, before any other part." 



Take again what E. H. A. says about lizards : — They 

 "once were great, the aristocracy of the earth. What a 

 strange world there must have been on this same earth of 

 ours in those days ! Did mosquitoes as large as sparrows, 

 with voices like tin trumpets, infest the swampy wastes 

 and torment the drowsy megalosaurus ; and did the winged 

 lizards, like flying foxes, hawk them in the dusky forests % 

 Did the mild iguanodon, when it had done browsing on a 

 tuft of maidenhair fern about the size say of a clump of 

 bamboos, turn round and waddle away into a hole, as its 

 successors do to-day on the plains of Guzerat ? The lizards 

 are the wrecks of a great past. They had their day ; 

 perhaps they abused it : at any rate th/e great unresting 

 wheel has gone round, and that which was up is down. 

 The commonalty do not seem to feel it much. But all the 

 descendants of great families, the crocodiles and alligators, 

 and even iguanas, are a prey to melancholy. They main- 

 tain a dignified spiritlessness which is affecting." " Like 



* " Tribes on my Frontier : An Indian Naturalist's Foreign 

 Policy." By E. H. A., witli illustrations by F. C. Macrae. 



