331 



SCIENTIFIC SIDE-LIGHTS 



{ncandescenc 

 ncredulity 



the Spaniards exported 64,350 hides from 

 that country and 35,444 from Santo Domin- 

 go, an indication of the vast numbers of these 

 animals which must then have existed there, 

 since those captured and killed could have 

 been only a small portion of the whole. 

 WALLACE Darwinism, ch. 2, p. 18. (Hum., 

 1889.) 



1617. INCREASE OF HEAT FROM 

 VIOLET TO RED AND BEYOND Throw- 

 ing a small and concentrated spectrum upon 

 a screen, by means of an endless screw we 

 move [a thermopile] . . . through the 

 entire spectrum, and determine in succession 

 the thermal power of all its colors. When 

 this instrument is brought to the violet end 

 of the spectrum the heat is found to be 

 almost insensible. As the pile gradually 

 moves from the violet towards the red, it 

 encounters a gradually augmenting heat. 

 The red itself possesses the highest heating 

 power of all the colors of the spectrum. 

 Pushing the pile into the dark space beyond 

 the red, the heat rises suddenly in intensity, 

 and at some distance beyond the red it at- 

 tains a maximum. From this point the 

 heat falls somewhat more rapidly than it 

 rose, and afterwards gradually fades away. 

 TYNDALL Lectures on Light, lect. 5, p. 189. 

 (A., 1898.) 



1618. INCREASE OF SURFACE IN 

 LUNG Device of the Diaphragm Respiratory 

 Power in Small Compass. In the lung of 

 man, as of mammals generally, an extraor- 

 dinary increase is given to the extent of 

 aerating surface, by the excessively minute 

 subdivision of the cavity into air-cells, of 

 which thousands are clustered round the end 

 of each terminal twig of the bronchial tree. 

 But this increase would be without effect 

 if there were not at the same time a most 

 elaborate provision in the skeleton of the 

 trunk, in the disposition of its muscles, and 

 in the mode in which these are acted on by 

 the nervous apparatus, for alternately filling 

 and emptying the lungs, so as to take in 

 fresh supplies of oxygen for the aeration of 

 the blood, and to get rid of the carbonic acid 

 which it gives off. The chief feature in this 

 provision is the enclosure of the lungs in a 

 distinct cavity (that of the chest) cut off 

 from the abdomen by a muscular partition, 

 the diaphragm, the contraction of which, 

 by increasing the capacity of the chest, pro- 

 duces an inrush of air down the air-pas- 

 sages, which penetrates to the remotest parts 

 of the minutely subdivided cavity of the 

 lungs. By no other action could the air 

 contained in that cavity be so effectually re- 

 newed. Thus the pulmonary apparatus of 

 the mammal is the most perfect form that 

 could be devised for obtaining the highest 

 amount of respiratory power within the 

 smallest compass. CARPENTER Nature and 

 Man, lect. 15, p. 461. (A., 1889.) 



1619. INCREASE, SIMULTANEOUS, 

 OF BUMBLEBEES AND MICE Fowls 

 Made Rapacious Mousers. In the summer 



of 1872-73 we had plenty of sunshine, with 

 frequent showers, so that the hot months 

 brought no dearth of wild flowers, as in 

 most years. The abundance of flowers re- 

 sulted in a wonderful increase of humble- 

 bees. I have never known them so plentiful 

 before; in and about the plantation adjoin- 

 ing my house I found during the season no 

 fewer than seventeen nests. The season was 

 also favorable for mice that is, of course, 

 favorable for the time being, unfavorable 

 in the long run, since the short-lived, un- 

 due preponderance of a species is invari- 

 ably followed by a long period of un- 

 due depression. These prolific little crea- 

 tures were soon so abundant that the dogs 

 subsisted almost exclusively on them; the 

 fowls also, from incessantly pursuing and 

 killing them, became quite rapacious in 

 their manner, whilst the sulfur tyrant-birds 

 (Pitangus) and the Guira cuckoos preyed on 

 nothing but mice. HUDSON Naturalist in 

 La Plata, ch. 3, p. 59. (C. & H., 1895.) 



1620. INCREASE, VAST POSSIBLE, 

 OF BIRDS Vast Consequent Destruction- 

 Slaughter Unperceived. Let us now con- 

 sider a less extreme and more familiar case. 

 We possess a considerable number of birds 

 which, like the redbreast, sparrow, the four 

 common titmice, the thrush, and the black- 

 birdj stay with us all the year round. These 

 lay on an average six eggs, but as several of 

 them have two or more broods a year ten 

 will be below the average of the year's in- 

 crease. Such birds as these often live from 

 fifteen to twenty years in confinement, and 

 we cannot suppose them to live shorter lives 

 in a state of nature, if unmolested; but to 

 avoid possible exaggeration we will take 

 only ten years as the average duration of 

 their lives. Now, if we start with a single 

 pair, and these are allowed to live and breed, 

 unmolested, tilj they die at the end of ten 

 years, . . . their numbers would amount 

 to more than twenty millions. But we know 

 very well that our bird population is no 

 greater, on the average, now than it was 

 ten years ago. . . . What, then, becomes 

 of the enormous surplus population annually 

 produced? It is evident they must all die 

 or be killed, somehow; and as the increase 

 is, on the average, about five to one, it fol- 

 lows that if the average number of birds of 

 all kinds in our islands is taken at ten 

 millions and this is probably far under 

 the mark then about fifty millions of birds, 

 including eggs as possible birds, must an- 

 nually die or be destroyed. Yet we see 

 nothing, or almost nothing, of this tremen- 

 dous slaughter of the innocents going on 

 all around us. WALLACE Darwinism, ch. 2, 

 p. 17. (Hum., 1889.) 



1621. INCREDULITY HINDERS IN- 

 VESTIGATIONAM Evidence of Meteorites 

 Once Rejected. That arrogant spirit of in- 

 credulity which rejects facts without at- 

 tempting to investigate them is in some 

 cases almost more injurious than an unques- 



