513 



SCIENTIFIC SIDE-LIGHTS 



Past 

 Patience 



nearly ten thousand. TYNDALL Floating 

 Matter of the Air, essay 3, p. 318. (A., 

 1895.) 



2523. Calculation of Time 



of Halley's Comet. Halley calculated, with 

 great pains, that the influence of the planets 

 would delay the next return of the comet, 

 and he predicted it for the end of 1758 or 

 the beginning of 1759. It was necessary, 

 with the improved mathematical formulae, 

 to calculate exactly the epoch of this return. 

 Clairaut undertook this, and performed in 

 a masterly manner the algebraical part of 

 the problem; but there remained the im- 

 mense task of calculating the formulae nu- 

 merically. Two computers had the courage 

 to do this the astronomer Lalande and 

 Madame Hortense Lepaute. During six 

 .months the two calculators, hardly taking 

 time to eat, put into numbers the alge- 

 braical formulae of Clairaut. Lalande fin- 

 ished the calculation, and found that Saturn 

 would delay its return by 100 days and 

 Jupiter by 518 days, in all 618 days' delay 

 that is to say, that its revolution would 

 be a year and eight months longer than its 

 previous revolution; and that, in fact, its 

 perihelion passage would take place within 

 a month of the middle of April, 1759. 



Never did scientific prediction excite more 

 lively curiosity from one end of Europe to 

 the other. The comet reappeared; it trav- 

 ersed the course announced among the con- 

 stellations; it passed its perihelion on 

 March 12, 1759, just a month before the day 

 indicated. " We have all observed it," wrote 

 Lalande, " so that it is beyond doubt that 

 comets are truly planets which revolve, like 

 the others, round the sun." Halley's comet, 

 in fulfilling the prediction of the astron- 

 omers, opened a new era in cometary as- 

 tronomy. FLAMMARION Popular Astron- 

 omy, bk. v, ch. 1, p. 486. (A.) 



2524. Identification of the 



Metals of the Sun. There have been iden- 

 tified, line for line, in the sun the 460 lines 

 of the spectrum of iron, the 118 of titanium, 

 75 of calcium, 57 of manganese, 33 of nickel, 

 etc., so that we now know certainly that 

 there are at the surface of that dazzling 

 star, and in the gaseous state, iron, tita- 

 nium, calcium, manganese, nickel, cobalt, 

 chromium, sodium, barium, magnesium, 

 copper, potassium; but we still cannot rec- 

 ognize any trace of gold, silver, antimony, 

 arsenic, or mercury. Hydrogen was discov- 

 ered in 1868. Oxygen must exist in this 

 furnace, but the oxygen lines which have 

 been found in the solar spectrum proceed 

 from our own atmosphere (Janssen, 1888). 

 FLAMMARION Popular Astronomy, bk. iii, 

 ch. 7, p. 326. (A.) 



2525. 



Minute Adjustments 



Delicacy of Eye and Hand. Nine years 

 later Dr. Henry Draper, of New York, got 

 an impression of four lines in the spectrum 

 of Vega. Then Dr. Huggins attacked the 

 subject again in 1876, when the 18-inch 



speculum of the Royal Society had come 

 into his possession, using prisms of Iceland 

 spar and lenses of quartz, and this time 

 with better success. A photograph of the 

 spectrum of Vega showed seven strong 

 lines. Still he was not satisfied. He waited 

 and worked for three years longer. At 

 length, on December 18, 1879, he was able 

 to communicate with the Royal Society re- 

 sults answering to his expectations. The 

 delicacy of eye and hand needed to attain 

 them may be estimated from the single fact 

 that the image of a star had to be kept, by 

 continual minute adjustments, exactly pro- 

 jected upon a slit T v of an inch in width 

 during nearly an hour, in order to give it 

 time to imprint the characters of its an- 

 alyzed light upon a gelatin plate raised to 

 the highest pitch of sensitiveness. CLERKE 

 History of Astronomy, pt. ii, ch. 12, p. 462. 

 (Bl., 1893.) 



2526. Tracing Gradations 



of Species. For five consecutive years I 

 have investigated this small but highly in- 

 structive group of animals [the calcareous 

 sponges] in all its forms in the most care- 

 ful manner. . . . With a view to these 

 facts, I made two journeys to the seacoast 

 (1869 to Norway, 1871 to Dalmatia), in or- 

 der to study as large a number of individuals 

 as possible in their natural circumstances, 

 and to collect specimens for comparison. 

 Of many species I compared several hun- 

 dred individuals in the most careful way. 

 I examined with the microscope and 

 measured in the most accurate manner 

 the details of form of all the species. As 

 the final result of these exhaustive and al- 

 most endless examinations and measure- 

 ments it appeared that "good species," in 

 the ordinary dogmatic sense of the system- 

 atists, have no existence at all among the 

 calcareous sponges; that the most different 

 forms are connected one with another by 

 numberless gradational transition forms; 

 and that all the different species of calcare- 

 ous sponges are derived from a single ex- 

 ceedingly simple ancestral form, the olyn- 

 thus. HAECKEL History of Creation, vol. i, 

 pref., p. 17. (K. P. & Co., 1899.) 



2527. PATIENCE OF ASTRONOMER 



- Vast Endeavor for Limited Result Five 

 Minutes' Observation the Reward of a Day's 

 Watching. The surface of the sun may be 

 compared to an elaborate engraving, filled 

 with the closest and most delicate lines and 

 hatchings, but an engraving which during 

 ninety-nine hundredths of the time can only 

 be seen across such a quivering mass of 

 heated air as makes everything confused 

 and liable to be mistaken, causing what is 

 definite to look like a vaguely seen mottling. 

 It is literally true that the more delicate 

 features . . . are only distinctly visible 

 even by the best telescope during less than 

 one-hundredth of the time, coming out as 

 they do in brief instants when our dancing 

 air is momentarily still, so that one who has 



