March 17, 1882.] 



KNOWLEDGE 



433 



stretching it open, he would, wth bis disengaged hand, take up the 

 chain and look which way (as he thouglit) it passed through, and, 

 by following the winding of the chain, would speedily untwist the 

 whole, to his utmost delight, and to the astonishment of those who 

 witnessed it. You can imagine the intelligence required when you 

 think of the difficulty overcome. He had to go outside the loop 

 evciy other turn. — F. Selby. 



PERSONAL ILLUSION. 



[336]— To me, horizontal lines appear much plainer thati perpen- 

 iHcular lines. Thus, I can tell the time by a clock more easily at, 

 ., 3. lo than at 6. So, also, the letters of printed words in small 

 no seem to touch each other; but, if I turn the page sideways, 

 • y oi)en out. Jliiuo. 



EXPLOSION" OF AMMONIA. 



337] — The explosion of a(|ua-ammonia.', related in Knowledge 



Fob. 10, reminds me of a similar occurrence in my own ex- 



rionce. A bottle of ammonia, baring the stopper tied down, had 



lained nndisturbod for some time in my photographic work- 



im. During some hot summer weather it burst with a loud 



plosion, and the contents were scattered in all directions. The 



It of the weathes, no doubt, liberated a quantity of ammonia 



-, which, being unable to escape, shattered the bottle. In the 



uunt of the accident detailed in Knowledge, the bottle of 



■itnionia is stated to have been kept on the mantelpiece, and to 



ve exploded in the woman's hand. A mantelpiece at this 



le of the year is presumably a very warm place, and if the 



|iper of the bottle had become fixed (as often li.appens), it is not 



l;ouk to under.stand how the heat of the woman's hand may have 



1 ved ''the last straw," the bottle having probably been almost at 



urstiiig point from the pressure of ammonia gas liberated by the 



ivurmth to which it was exposed on the mantel-piece. It is impos- 



-ibie to Buppo.se that an aqueous solution of ammonia could b? 



\plosive in the usual sense of the word, and I think the above 



must be t ho true explanation of the accident, and a source of danger 



« hich jierhaps few are aware of. B. A. (Cantab.) 



!1C)\V' TO PRESERVE FOSSILS, BONES, &c., FROil THE 



ACTION OF THE AIR. 



338] — 1. See that the fossils are washed free of all efflorescence, 



rt. lie. and well dried. 2. Take strong Scotch glue 4oz. ; dissolve 



u'luo-kettle, with enough water to make a thick mucilage. Then 



i i 1 oz. of boiled linseed oil, stir well ; dissolve J oz. of bichromate 



1 potass in a small quantity of water, and add this to the glue, then 



iliiii down with water to the consistency (while hot) of milk. 3. 



Put the dried fossils or bones into an oven and make them very 



lit, then drop them into the boiling solution and keep them near 

 r simmering point for half-an-hour. Wipe them with a sponge 

 I'l oxiiosc them to dry in the air and sunshine. If properly 

 iiiaged tliey will now keep indefinitely. 



I'.S. The above prepared glue, of the proper thickness, is the best 

 iiig for repairing broken fossils, and for making any joints required 

 lie strong and good. F. 



A SERIES OF ASTONISHING COINCIDENCES. 



339] — In connection with the editor's papers on chance and 

 incidence, the following remarkable instance of purely fortuitous 

 incidence will be of interest. About a month since a friend of 

 i:ie, Mr. Hunt, went to a small town, about twelve miles from 

 'ter, to attend a meeting, returning home the same night. 

 • ile there he called upon the Rev. J. Smith, remaining about an 

 ir. Just before leaving, the postman called at the house, and a 



; er was brought in addi-essed "Mr. J. P. Hunt, C ." The 



I \'ant said to her master, " Please, sir, the postman wants to 

 uw if you know who this letter is for, as he does not know the 

 .me in the to^vn." As it was distinctly addressed to my friend. 

 In: opened it, and found it was from a chum of his in the North of 

 England. I may say that the letter contained nothing whatever of 

 importuiHO. A few days afterwards another letter arrived (at his 

 proper .iddress) from the same fellow, saying : "1 wrote you last 

 week, but, of course, you never got the letter, for, like an ass, 1 



directed to C ■, of all places in the world." I should say that; 



Mr. Hunt; had nothing whatever to do mth C . The postman 



knew nothing at all about him, and he was not expected at Mr. 

 Smith's. So that the purely fortuitous character of the circum- 

 stances that guided the misdirected letter to his hands is complete. 



H. Snell. 



BKIOHTNESS OP TELESCOPIC IMAGES. 



[310] — In a review of Professor Newcombe's work in Knowledge, 

 the common opinion that large telescopes increase the brightness of 

 objects having visible surfaces is stated to be erroneous. Is this so 

 in all cases ? Let the brilliancy of the retinal imago of (say) the 

 moon be tmity. Then, with a telescope having thirty-six times the 

 light-gathering surface, the image at the focus is thirty-six times as 

 bright. If I magnify this imago nine times superficial, the magnified 

 imago is one-ninth as bright ; but the image at focus is thirty-six 

 times as bright as the retinal inuige. Therefore, the magnified 

 image is thirty-six ninths, or four times, as bright as the retinal 

 image. If I increase the aperture and retain the same magnifying 

 power, the image should bo brighter still. No doubt I am astray 

 somewhere, and should esteem it a favour if you would kindly point 

 out where. Thanking you for past favours. W. Kidd. 



[\ou will find that where magnifying power is less than increase 

 of illuminating power, the eye can only i-eceive a portion of the 

 emergent pencils. My friend Dr. Huggins had an old telescope 

 intended to give great increase of light (a night glass), and he 

 found the emergent pencils were an inch in diameter — as, ho said, 

 " a telescope for a horse, not for a man." — Ed.] 



THE OWNER OF THE CORONA. 



[341] — I was present at the birth of the nurseiy rhyme to which 

 you refer in your last number, and can vouch for the original form 

 in which it appeared. The part in question ran thus : — 



[Our correspondent must excuse our omitting the first two lines 

 and the last; which are to some degree jiersonal. — Ed. J 



He thought himself owner of half the Corona, 



The rhymes were made by Dr. Thorpe, a member of the Sicilian 

 Eclipse Expedition of 1870. On leaving Poretta, a station between 

 Verona and Florence, Professor Clifford commenced making nursery 

 rhymes on the names of the stations taken from Bradshaw, and Dr. 

 Thorjje carried on Professor Clifford's idea by rhyming the names of 

 the members of the expedition. There is a moderation about the 

 origiral recension which recommends itself to my judgment. It 

 will bo noticed that the claim set up is only to the ownership of 

 " half of the Corona." The verses were received with great applause 

 by the members of the Eclipse Expedition, who had been travelling 

 with the " owner " for some days. Mr. Rand Caprou's version mast 

 have been derived from an inaccurate source — perhaps the owner 

 subsequently saw his way to improving tbem. 



A Member of the Sicilun Eclipse Expedition. 



INTERIOR HEAT OF THE EARTH. 

 [342] — Your correspondent, " B." (No. 287), will find, if he 

 refers to the Rev. Osmund Fisher's recentlv-published work on the 

 " Physics of the Earth's Crust," that Professor Mohr's speculations 

 have not escaped the notice of scientific men in this country. He 

 will also find his deductions from the observations made in the 

 bore-hole at Sperenberg very ably combated by Mr. Fisher in the 

 above work. — I am, your obedient servant, D. C. W. Hike. 



EARTH'S INTERNAL TEMPER.A.TURE. 



[313] — I have not seen Professor Mohr's book, but 1 recollect the 

 inference he attempted to draw from the temperature observations 

 at the Sperenberg borehole. It is altogether fallacious, and the error 

 has been pointed out by Professor Everett in the " Report of the 

 Committee of the British Association on Underground Tempera- 

 tures," and by the Rev. 0. Fisher in his work on the " Physics of 

 the Earth's Crust." In almost any book on geology — say, " Coal : 

 its Uistorj' and Uses" (Macmillan), " B." Avill find an account of 

 the result of the examination of coal plants by competent 

 botanists. 



A single instance of asphalte in granite is rather slender evidence 

 for disputing the generally-received views as to the origin of that 

 rock. It may have been a case in which granite has been formed 

 by the intense mctamorphism of a rock containing bituminous 

 matter, and if the change was effected deep down under ground, 

 the ])res3ure may well have prevented volatilisation and escape. — 

 A. H. G. 



THE RAINBAND. 



[344] — I observe in a recent number the discover^• of this band 



in the spoctroscojie is given to Piazzi Smyth, which may be true, as 



there is no date affixed, but if so it must have been before April 20, 



1871. On that date Professor James Cooke asked me if 1 had noticed 



