169 



SCIENTIFIC SIDE-LIGHTS 



fiffi, 



cause of all the phenomena exhibited is 

 found to be the escape of steam from the 

 midst of masses of incandescent liquefied 

 rock. The violence, and therefore the 

 grandeur and destructive effects, of an erup- 

 tion depend upon the abundance and tension 

 of this escaping steam. JUDD Volcanoes, ch. 

 2, p. 31. (A., 1899.) 



824. DIFFERENCES, ABSOLUTE 

 AND RELATIVE Moonlight vs. Sunlight- 

 Darkening Shadow Has the Effect of In- 

 creasing Light. If we compare the shadow 

 thrown by an object in moonlight with the 

 shadow cast by the same object in sunlight, 

 it will be at once seen that the former ap- 

 pears much darker than the latter. In a 

 landscape seen by moonlight, this stronger 

 contrast of light and shade makes the illu- 

 mination far brighter, altho it is absolutely 

 much less intense. And from this fact we 

 can distinguish at the first glance whether a 

 picture represents a moonlight or a day- 

 light scene. It is not in the power of the 

 artist to mark this difference by an abso- 

 lute difference of light-intensity. Both his 

 paintings are equally bright; but he makes 

 the difference between light and shadow 

 greater in the first picture than in the sec- 

 ond, and by this single device enables us to 

 distinguish in a moment the night scene 

 from the day scene. WUNDT Psychology, 

 lect. 4, p. 58. (Son. & Co., 1896.) 



825. DIFFERENCES AMONG ANI- 

 MALS IN THE PHILIPPINES Supposing 

 that a long chain of islands had connected 

 two lands lying far apart and differing 

 widely in their fauna, it might be expected, 

 and with great probability, that the fauna 

 of this group could have retained no special 

 homogeneous character. For the vicinity of 

 the two terminal countries, and the currents 

 probably existing, might easily have caused 

 on the islands a mixture of the two dis- 

 similar faunas. This is, in fact, sometimes 

 the case. The Philippines lie very nearly 

 north and south; the northern islands are 

 connected with China by the Bashees and 

 Formosa, while the southernmost island, 

 Mindanao, is connected by Celebes and some 

 smaller islands with the Moluccas, and the 

 southwestern island, Palawan, hangs on to 

 Borneo by Balabac. ... A greater con- 

 trast can hardly be conceived of than that, 

 for instance, between the fauna of Hong- 

 kong, Amoy, or even Siam, on one side, and 

 Borneo, ^ Java, and Sumatra, on the other. 

 And this difference is repeated in a very 

 striking manner in the Philippines, where 

 the northern district displays an unmistak- 

 able harmony with the true Chinese fauna, 

 while the southern islands show a marked 

 resemblance partly to Borneo, partly to 

 Celebes and Gilolo, and partly to the west- 

 ern islands of the Australian region. SEM- 

 PER Animal Life, ch. 9, p. 283. (A., 1881.) 



826. DIFFERENCES BETWEEN MAN 



AND APE An Unbridged Chasm No Inter- 

 mediate Link. Thus, whatever system of 



organs be studied, the comparison of their 

 modifications in the ape series leads to one 

 and the same result that the structural 

 differences which separate man from the 

 gorilla and the chimpanzee are not so great 

 as those which separate the gorilla from the 

 lower apes. 



But in enunciating this important truth, 

 I must guard myself against a form of mis- 

 understanding which is very prevalent. I 

 find, in fact, that those who endeavor to 

 teach what Nature so clearly shows us in 

 this matter are liable to have their opinions 

 misrepresented and their phraseology gar- 

 bled until they seem to say that the struc- 

 tural differences between man and even the 

 highest apes are small and insignificant. Let 

 me take this opportunity, then, of distinctly 

 asserting, on the contrary, that they are 

 great and significant; that every bone of a 

 gorilla bears marks by which it might be 

 distinguished from the corresponding bone 

 of a man ; and that, in the present creation, 

 at any rate, no intermediate link bridges 

 over the gap between homo and troglodytes. 



It would be no less wrong than absurd to 

 deny the existence of this chasm; but it is 

 at least equally wrong and absurd to exag- 

 gerate its magnitude, and, resting on the ad- 

 mitted fact of its existence, to refuse to in- 

 quire whether it is wide or narrow. HUX- 

 LEY Man's Place 'in Nature, p. 232. (Hum.) 



827. DIFFERENCES OF INSTRU- 

 MENTS FOR STUDY OF THE HEAVENS 



The Transit Instrument and the Equa- 

 torial Each Has Its Own Special Value 

 Analogy of Spiritual Gifts (1 Cor. xiii, 4-6; 

 Rom. xii, 6-9 J. There are two chief modes 

 of using the telescope, to which all others 

 may be considered subordinate. Either it 

 may be invariably directed towards the 

 south, with no motion save in the plane of 

 the meridian, so as to intercept the heavenly 

 bodies at the moment of transit across that 

 plane; or it may be arranged so as to fol- 

 low the daily revolution of the sky, thus 

 keeping the object viewed permanently in 

 sight, instead of simply noting the instant 

 of its flitting across the telescopic field. The 

 first plan is that of the "transit instru- 

 ment," the second that of the "equa- 

 torial." . . . 



The uses of each are entirely different. 

 With the transit, the really fundamental 

 task of astronomy the determination of the 

 movements of the heavenly bodies is main- 

 ly accomplished; while the investigation of 

 their nature and peculiarities is best con- 

 ducted with the equatorial. One is the 

 instrument of mathematical the other of de- 

 scriptive astronomy. One furnishes the ma- 

 terials with which theories are constructed, 

 and the tests by which they are corrected; 

 the other registers new facts, takes note of 

 new appearances, sounds the depths and 

 pries into every nook of the heavens. 

 CLERKE History of Astronomy, pt. i, ch. 6, 

 p. 149. (Bl., 1893.) 



