April 23, 1886.] 



SCIENCE. 



367 



dazzling brightness at least 

 five or six times that of the 

 neighboring portions of the 

 photosphere, and moved 

 eastward over the spot in 

 parallel lines, growing 

 smaller and fainter, until in 

 about five minutes they dis- 

 appeared, after traversing 

 a course of nearly thirty-six 

 thousand miles." 



YOUNG (p. 267). 



". . . the temperature at 

 the focus can not rise above 

 that of the source of heat, 

 the effect of the lens being 

 simply to move the object 

 at the focus virtually to- 

 ward the sun; so that, if we 

 neglect the loss of heat by 

 transmission through the 

 glass, the temperature at 

 the focus should be the 

 same as that of a point 

 placed at such a distance 

 from the sun that the solar 

 disk would seem just as 

 large as the lens itself 

 viewed from its own focus. 



" The most powerful lens 

 yet constructed thus vir- 

 tually transports an object 

 at its focus to within about 

 two hundred and fifty thou- 

 sand miles of the sun's sur- 

 face, and in this focus the 

 most refractory substances 

 — platinum, fire - clay, the 

 diamond itself— are either 

 instantly melted or dissi- 

 pated in vapor. There can 

 be no doubt that, if the sun 

 were to come as near us as 

 the moon, the solid earth 

 would melt like wax." 



apart: these suddenly burst 

 into view near the edge of 

 a great sun - spot, with a 

 brightness at least five or 

 six times that of the neigh- 

 boring parts of the sun. and 

 travelled eastward over the 

 spot in parallel lines, grow- 

 ing smaller and fainter, un- 

 til in about five minutes 

 they disappeared, after a 

 journey of about thirty-six 

 thousand miles." 



BALL (p. 495). 

 ". . . the temperature at 

 the focus cannot be greater, 

 cannot be even equal, to the 

 temperature at the source 

 of heat itself. The effect of 

 a burning-glass is merely 

 equivalent to making a 

 closer approach towards the 

 sun. The rule is indeed a 

 simple one. The tempera- 

 ture at the focus of the 

 burning-glass is the same as 

 that of a point placed at 

 such a distance from the 

 sun that the solar disk 

 would seem just as large as 

 the lens itself viewed from 

 its own focus. The greatest 

 burning-glass which has ever 

 been constructed virtually 

 transports an object at its 

 focus to within 250,000 miles 

 of the sun's surface : in other 

 words, to a distance of 

 about l-400th part of its pres- 

 ent amount. In this focus 

 it was found that the most 

 refractory substances, 

 agate, cornelian, platinum, 

 fire-clay, the diamond itself, 

 were melted or even dissi- 

 pated into vapour. There 

 can be no doubt that if the 

 sun were to come as near to 

 us as the moon, the solid 

 earth itself would melt like 

 wax." 



By what name Dr. Ball would call this whole- 

 sale pillaging of others' books, we do not know ; 

 but it seems to us to fall little short of tallying 

 with the work of the plagiary. Substituting 

 'greatest bmning-glass ' for 'most powerful 

 lens,' and adding agate and cornelian to a list 

 of refractory substances already fully long- 

 enough for the purpose of illustration, do not 

 show any mark of great originality, while the 

 continued effort to conceal the theft is petty in the 

 extreme. We have not had the time to trace Dr. 

 Ball's possible liberties with other authors than 

 these, but our researches thus far have left us in 

 the mood for suggesting that the titlepage of sub- 

 sequent editions of his work might with some 

 little show of justice contain the insertion ' com- 

 piled by .' Any one who cares to investigate 



further may perhaps like to judge for himself 



how much of pp. 495 - 505 in Dr. Ball's very in- 

 teresting chapter on the ' Astronomical signifi- 

 cance of heat ' (the greater part) was directly sug- 

 gested by a like number of pages at the end of 

 Professor Young's chapter on the ' Sun's light and 

 heat.' While in another part of his book Dr. 

 Ball alludes to Professor Young as ' the well- 

 known authority,' etc., in the chapter in question 

 we find no mention of the name. Professor 

 Young would doubtless be very glad to be of as- 

 sistance to Dr. Ball, but we think he is human 

 enough to care for the graceful acknowledgment 

 of the service. 



GEOGRAPHICAL NOTES. 



Dutch statistics of population. — Kuyper has 

 recently given an interesting discussion of the 

 population-statistics of the Netherlands. The 

 population for the whole kingdom is found to be 

 121.6 per square kilometre, and 75.0 for the low- 

 lands, and varies from 265.9 to 44.6 for the same 

 area in different districts. The females out-num- 

 ber the males by from one to two per cent. Of the , 

 population, 32 per cent are married ; 61.55 per 

 cent are Protestants, 36.02 are Catholics, and 

 2.04 per cent are Israelites, in religion ; and, in 

 occupation, 20 per cent are agriculturalists, 26 

 per cent laborers, 12 per cent merchants, 18 per 

 cent manufacturers or mechanics, 2.5 per cent 

 soldiers, 2.3 per cent engaged in religious, scien- 

 tific, or sanitary professions. The increase of 

 population from 1860 to 1880 varied from 12 per 

 cent, in Limburg, to 30 per cent, in Holland 

 proper. Of thirty-eight centres of over 10,000 

 inhabitants, one (Delftshaven) has doubled, seven- 

 teen have increased more than 25 per cent, and 

 twelve others have increased from 10 to 25 per 

 cent, during the same period. The work is sup- 

 plemented by an instructive chart showing the in- 

 crease of population for the period by single 

 parishes, — a course only practicable in so small a 

 country as Holland. 



Search for mammoths in the Lena Delta. — 

 Dr. Bunge has sent to St. Petersburg a chart of 

 the Lena Delta, corrected during the numerous 

 long journeys undertaken by him in search of 

 frozen mammoths. His travels were more lucky 

 geographically than biologically, for he found but 

 one skeleton, and that deprived of head and one 

 fore-leg. It had been exposed for ten years to 

 the attacks of dogs, foxes, and natives, but had 

 originally been covered with a thick coat of hah', 

 which might have defended it against even the 

 present climate of the delta, provided it could 

 have obtained food to its liking. 



Medals of Paris geographical society. — The 

 great gold medal of the Paris geographical so- 



