42 



♦ KNOWLEDGE ♦ 



[July 20, 1883. 



point v over that of the point G, during that interval ; or 



py2^Vv/-^- "^ ' 



:. total westwardly deflection 

 2- /-o / 



= ^^(2/1=- iicA 

 py2</V ^ / 



_ 8-A"^ _ i-h /ill _ i-h^ 

 iV^/Yy 3P V r/ 3p ' 

 or westwardlv deflection during ascent and descent 



3P ' 

 as before. 



The real deviation, as shown at pp. 10, 11, is twice as 

 great. The error manifestly arises from our not taking 

 into account the fact that gravity does not act throughout 

 the flight at right angles to the course which the body 

 originally possessed in a horizontal direction. In our next 

 we shall consider the problem analytically with due 

 reference to this point, which, though it may seem slight, 

 really causes the deviation to be twice as great as it would 

 be were the directions of gravity on the falling body parallel 

 throughout the flight. 



A Contemporary says that by a recent analysis of 

 tobacco-smoke, M3I. G. Le Bon and G. Xoel have ex- 

 tracted bottles of — (1) Frussic acid ; (2) an alkaloid of an 

 agreeable odour, but dangerous to breathe, and as poisonous 

 as nicotine, since one-twentieth of a drop destroys animal 

 life ; (3) aromatic principles, which are as yet undeter- 

 mined, but which contribute, with the alkaloid, to give the 

 smoke its perfume. The alkaloid appears to be identical 

 ■with collidine, which has been observed in the distillation 

 of many organic substances, but its phj-siological and 

 poisonous properties have been hitherto unknown. 



Floating Domes foe Telescopes. — The Paris Obser- 

 vatory, requiring for a new telescope a dome 20 metres, 

 or rather more than 6.5 feet 7 inches in diameter — the size 

 of that of the Pantheon — it was resolved to accept a 

 proposal of Eitfel to make it float in an annular tank, to 

 be tilled with water containing chloride of magnesium, to 

 prevent its freezing in the winter. This being mentioned 

 as quite a novelty in a Report of the Observatory issued 

 in February, M. Merten explains in Ciel. et Terre that a 

 floating structure was proposed by Van Rysselberghe in 

 1880, and accepted in May, 1882, for the new Observatory 

 in the environs of Brussels, with some improvements in 

 detail devised by MM. Eoyers, engineers to the city of 

 Antwerp. There is to be an annular tank, filled with a 

 mixture of three parts of water and one of glycerine, and 

 in it a float of corresponding shape, carrying a cylindrical 

 superstructure, with a sliding-roof opening half way. By a 

 simple mechanism, the whole cylinder will have a revolving 

 motion, and also be capable of elevation and depression, 

 so that when required the telescope may be completely 

 uncovered. 



€iiitorial (gosstp. 



Readers of Knowledge may, perhaps, be interested to 

 learn how pleasantly and successfully the holiday lectures, 

 which began with my course of six at St. Leonards-on-Sea, 

 are progressing. We have begun with the south-east of 

 England, and are working steadily westwards and north- 

 wards at present, though it is probable that we shall return 

 to some of the places where we have been most agreeably 

 greeted. At present (Saturday, July 1-lth) thirty-five of 

 these summer lectures have been given at St. Leonard's-on- 

 Sea, Tunbridge Wells, Eastbourne, Worthing, Folkestone, 

 Brighton, Dover, Deal, Portsmouth, Ashford, and Chi- 

 chester. 



Although I have been pleased, and even surprised, 

 considering the season, at the welcome given me at all 

 these places, I have had to note at some of them — especially 

 at Chichester, Ashford, and Deal, a rather amusing slow- 

 ness of apprehension, not in those who have come to the 

 lectures, but in those who have not come. I get multi- 

 tudes of letters after I have left a place, telling me how 

 gladly the writers would have come to the lectures if they 

 had known that they were so easily to be understood even 

 by persons not much acquainted with astronomy. They 

 find this out rather late, considering I have lectured now 

 for nearly fourteen years, and always on the same plan. 

 Then they ask me to return, either repeating my lectures 

 or giving others of the series. But of course it is pre- 

 cisely to the places where these erroneous ideas have pre- 

 vailed that I am least likely to return. I might possibly, 

 at a second visit, see those who, "had they but knowTi," itc, 

 as they write, would have attended the first series ; but 

 though that might suit them, it would be very incon- 

 venient to me. It is not only as easy to address a thousand 

 as to address five hundred, but far easier — to say nothing 

 of the circumstance that if the thousand divide into two 

 audiences of five hundred, all expenses are doubled. 



Then, as to time ; we calculate that to work through 

 England and Wales, Scotland, and Ireland, as we propose 

 to do, will take not less than two years, and that is all the 

 time I can spare. I put ofl' my return to America till the 

 autumn of 1885, but I can put it no further oS. Therefore, 

 though exceptional success may encourage me to return to 

 certain places, or to give more lectures than I had originally 

 intended, it is impossible for me to make two ^dsits to 

 places where half of those who wish to hear me only find 

 out their wish after I have left. 



In the last number but one appeared a short extract from 

 the Spectator (from the pen, I imagine, of Mr. Richard H. 

 Hutton), headed "God's Will." This has caused some cor- 

 respondents to send me a few very singular letters. When 

 I receive a single particularly foolish letter on a subject, I 

 generally assign it to some " local lunatic " who has been 

 unwisely entrusted with pen and paper. But when 

 several such letters appear, I begin to think there is some 

 reason for their writers' mistakes. Yet in this case, what 

 can be the reason 1 A writer thoughtfully propounds 

 anew the old, old mystery, the existence — nay, the general 

 prevalence — of evil. Stating at the outset his belief that 

 God governs as well as reigns, he shows what a mystery 

 God's government is. He points to the vast, unending, 

 inexplicable waste of life, to the miseries endured by 

 too many of those who live, and shows that for us there 

 is no solution to the awful problem. On this, there fall 



