06 



• KNOWLEDGE • 



[Dm 2, 1881, 



SOLAU HEAT. 

 rSC] — HoforrinR to I^cttrr 2 (ynga 15), I am of opinion ttiiit 

 wliiitovrr conditions iipi'lv to this ciirtli npply also to tlir sun, only 

 in n (^rontor tli'^jn-o. Tlii' mnltor of which iho iiirth (and all the 

 |iliinctH anil Hatcllitcs) is composed, onco formed jiart of the sun, 

 which has (frnilnally condensed and left each ]>lanet behind in its 

 Inm, Geolof^ists tell lis that at a period inccmceivably remoto our 

 t,'Iol>e was in a state of intense heat, 'niis is i)ractical proof that 

 the sun is in a similar state. Ri'ferrin^j to Letter 28 (paRO 58), Mr. 

 Nowton Crosland endeavours, by one fell blow, to anniliilato the 

 KTpat law of universal gravitation. In promulgating tliis great law, 

 Newton cleared away heaps of tho cumbrous rubbish with which 

 the old schools of astronomy were hampered. Emerson says : " Tlio 

 tendency of all science is to 8ini|)lify." Mr. Crosland endeavours to 

 complicate. — Yours, &c., John Tiio.mson. 



IS TUK SUN UOT? 



[67] — It may interest your readers to know that this subject was 

 discussed in Desitin mid U'nrk, Vol. VII., under the question, " Does 

 the Sun Warm tho Earth?" Tho leader of that discussion en- 

 deavoured to prove that we receive our heat from tho earth, and 

 nut from tho sun ! Under tho title of " Tho Great Primordial 

 Korce," it has also received tho attention of Henry Raymond 

 Rogers, M.D., of Dunkirk, X.Y., in a paper published in tho 

 September number of /'I'o^irss of Science. In this paper, Dr. 

 Rogers propounds a similar oi>inion to that eipressed by your coitc- 

 spondent, " Co^ito," in letter 21. G. E. Bonney. 



THE SUN'S HEAT AND THE EARTH'S RADIATION. 



[68] — I have read the replies to Anti-Guebre's question (which, 

 like yourself, I have freqneutly encountered before) ; but in all of 

 them, including your own, one important factor is omitted — viz., the 

 difference between the obstructive or absorbent power of atmo- 

 spheric vapour to the raj'S of heat from different sources. Tho 

 sun-rays, as several correspondents have stated, pass tlirongh our 

 ordinary atmosphere with but little al)Sorj)tion ; but this is not the 

 case with *' obscure rays," or rays from a less heated and non- 

 luminous source. Hence the earth warmed by the sun doos more 

 to wann the air than tho sun itself does, because tho heat it 

 radiates is absorbed by the air, and also because it warms tho 

 air by direct contact and the commingling of tho portion of 

 air thus heated with that above, or " convection." It appears to 

 me that even our best treatises give too much credit to tliis 

 latter action, and too little to the first. Tho following 

 experiment which I tried many years ago ou Slont Blanc, at an 

 elevation of between fourteen and fifteen thousand feet, is instruc- 

 tive. My coat was wettod bv falls on tho sloppy surface of tho 

 glacier Ijelow, and at the elevation above-named, I noticed that the 

 coat-tail opposite the sim was thawed, while that in the shade was 

 frozen and stiff. By slowly turning round like a joint of meat 

 before a roasting fire, I alternately thawed and refrozo all sides of 

 my coat-tails in about one minute, as nearly as I can remember. 

 The direct rays of the snn woro painfully scorching, and skinned 

 my face and ears completely, but in tho shado, tho thin and highly- 

 dried air ponnittod a far greater degree of radiation of obscure 

 beat to tnko place than down below. Hence the freezing. I do 

 lint write this to controvert the other explanations given by your- 

 self and correspondents, but merely to supjily an additional factor. 



Thus, the cooling effect of night radiation is far raoro effective 

 above than below, seeing that the amount of resistance to tho 

 passage of tho obscure rays is so greatly diminished there. This 

 is strikingly shown by tho sudden freezing of tho rills and stream- 

 lets, which are such remarkable features of a glacier surface during 

 the summer's day. They all stop as the .sun sets, and tho sloppy 

 surface of ice is dried, as waa the shady siile of my wot coat. 



W. M.\TTiEU Williams. 



LIGHTNING IN NOVEMBER. 



[69] — Last night (Nov. 4) at 10.30 p.m., in a perfectly cloudless 

 sky, tho flashes of sheet lightning were vivid and incessant. Is not 

 this very unusual at this lime of tho year ? A strong gale was 

 blowing in the Irish Channel at the time.— Yours, A-c, 



Liv.ri>o(,l, .Y,;,r. 23, 1881. E. S. 



LOGARITHMS. 



[70] — Mr. Grundy asks for information on an important item in 

 connection with Logarithmic work, viz., the tables. Many students 

 give up in disgust this simple procesis of calculation bocouso they 

 have been unfortunate in their choice of books. 



I have been in tho habit of using Logarithm Books for many years, 



for work of every description, and with pleasure give him my 

 exporienco. 



In a long seriea of logarithmic calculations, the bo<jk to uflo will 

 depend on the number of figures wo re<iuire in tho desirofl result. 

 For instance, in doing ■t-flgnro work, it would Ixs a loss of lalxiur 

 and tinio to uso a 7-tiguro table. 



Tho following are tho tables I have u-sed with great comfort]: — 



For i-J>;;iire Wnrk; — 



Table of Lnyit and Atitt-Logii, published by Ijiyton, price Is. (Ver)- 



nsoful.) This requires simple interpolation. 

 Table of Logs and Anti-Loga (Uannyngton), published by Layton, 

 ])rico 58. A comfortable table, bnt rather dear. 

 For B-fi'jiire TVork : — 

 Table of Logs, published by Smith, Elder, 4 Co., price iB. 6d. A 



good book, and well worth the money. 

 Table nf Logs bij Oavnn. Better than the above, bnt requires a little^ 

 more practice. It contains many other useful tables. Can be- 

 had of Triibner, i>rice about Is. Od. 



For 7-f 'jure TVork:— 

 Table of Logs by Bruhns. Tho best book published ; I strongly 

 recommend it. Can bo had of Triibner, price about 4a. or less. 

 Table of Anti-Logs by Filipowski. This is a useful book when many 

 Anti-Logs are required. Published by Bell & Daldy. 



Abaci's. 



THE PRIMARY COLOURS. 



[71] — In the little Treatise on Optics, forming part of the conrso- 

 of " Natural Philosojihy," published in 1862, by the Commissioners 

 of National Education in Ireland, a statement is put forward with 

 respect to tho constitution of the solar spectrum, which differs from 

 that set forth in other similar works upon chromatics. 



The correctness of that statement is borne out by what I myself 

 conceive to be the appearance of tho character of the colour of 

 violet light, yet I confess I am puzzled to make out how, upon the- 

 explanation offered, the colour of the light in question is to be 

 accounted for. 



Tho commissioners, after describing in detail Newton's experi- 

 ment of breaking up solar light into its seven coloured constituents, 

 continue their statement as follows : — 



'' In reality, blue, rod, and yellow are the only colours present, the 

 rest being combinations of them. For the spectrum consists of a 

 layer of each of these colours, superimposed on the other — the blue, 

 tho red, and the yellow apj>earing distinctly at those points at which 

 they are most vivid in tho superimposed and corresponding layers." 



" Tho three colours of which tho spectrum is really composed arc 

 thus divided among tho seven which it contains, calling red rays R. 

 yellow Y, and blue B. 



White Red. Orange. Qreon. Blup. Indiijo. Violet. 



20R-i-3OY-f50B 8R 7R + 7Y -lOY + lOB 7Y-I-12B 12B 16B + 5B.' 



Thus far tho commissioners. 



As I have said, tho impression produced on my eyo bears out dis 

 tinctly the statement as to tho occurrence of red light in the violol 

 exhibited by a really pure prism of dense flint glass. Yet if tl) 

 spectrum con.sista simply of tho layers of the three colonra a 

 question superimposed, it is difficult to conceive what appearane 

 each of those spectra would present, could wo manage to obtoinit 

 isolated. In what form, for instance, would tho red spectim 

 present itself ? From tho above table we learn that no red exits 

 in the yellow, green, blue, or indigo, while a considerable amountof 

 red is met with again in tho violet. Wouhl the rod spectrum oxhi>it 

 a wide, blank interval, extending from the yellowish end of ho- 

 orange up to tho violet end of the blue ? 



An explanation of this matter, "plainly worded, exactly Ic- 

 scribcd," will doubtless bo an easy task for you, and will iiroboly 

 prove a boon to others besides, 



Yours, A-c, 



Mabel Wi.npbed L.us. 



PHRENOLOGY. 



[72] — Will you allow me to make a few observations, in aswcr 

 to tho first query contained in letter 32, p. 50, entitled " Pkeno- 

 logy " ? " G. P." says : "Assuming that phrenology is all 'rong. 

 what are the causes that determine the shape of tho head' " I 

 would observe at the outset that if we assume i)hrcnology to b " all 

 wrong," there can bo no satisfactory explanation given of thtdiver- 

 sities in tho shapes of heads. A common answer to tho query" ^Vhy 

 aro no two heads alike 'f " is, " Why aro no two faces o! hands 

 alike?" Tho simplest answer to this last seoms to be, hat no 

 two human natures are alike, and this will apply to to first 

 also, when wo consider that tho varieties we discover in tho 



[Con/iilBn* on nge 99. 



