Friction and Percussion. Messrs. Editors :On page 246 of your issue of October 16, the re is an article on “ Heat, and its Relation to Friction and Percussion a propose, and in favor of the vibratory theory. While I am not at all disposed to take issue with the writer, “ Spectrum,” I must b..g to differ from him in deductions from some of the cases offered. He holds that the heating of a nail held upon a grindstone is the result of the percussion arising from the jumping of the iron from one particle of the stone to the next, and estimates, indirectly, that m the majority of instances heat claimed to arise from friction is the result of percussion instead, Let “ Spectrum “ hold an old-fashioned brass-headed tack or a smooth brass button between his thumb and finger, and rub it briskly up and down the grain ' of a planed pine board until he can guess at the amount of percussion produced, and, in my opinion, he will drop the button if he does not the theory, before he flnishes the calculation. The heat conductibility of the metal suggests an illustration relative to the heating of the nail by rapid blows of a light hammer, when slower, but heavier blows failed to raise the temperature of a nail, alluded to by “ Spectrum." Several years ago a hammered horse nail machine, now in successful operation at Falls Village, Mass., came near proving a total failure because the nails would cool before they were finished; and it was finally discovered that in slow hammering the long contact of the hammer with the heated nail conducted away the caloric, while sharp, quick blows tended to raise rather than lower the heat. Will “ Spectrum “ please inform me why it is that while iron can once be heated in this way by percussion, but, if suffered to cool, the heat cannot be reproduced in the same manner, until after the iron has been heated by the absorption of foreign caloric ? Then the experiment can be repeated. New Albany, Ind.C. C. H. How tOo Observe tbe Sun. Messrs. Editors :On page 139, present volume, your article, “ Storms in the Sun,” shows conclusively that visible disturbance there is instantly followed by electric disturbance here. A regular daily record of the visible state of the sun, compared with our meteorological records, might lead to important discoveries. Believing that a simple means of observing and accurately recording solar phenomena would induce amateurs as well as professionals to keep such records, I respectfully propose the following method, which I have never heard of being thus used by any one before : Take an astronomical .refracting telescope, with Huyghenian eye piece, into a dark room, direct it on the sun through an aperture, push in the eye piece until it is between the object glass and its principal focus; now place a fine white screen at some distance from the eye piece and focus sharply; a large, clear, well defined, erect image of the sun is thus obtained. which may be enlarged or diminished at will; arrange tile aperture, increasing or decreasing the light until the finest details are v'sible. The sun can now be examined without darkening glasses, and by several persons at once. For unif irmity of record, I would suggest the adoption of one regular size, say a circle inscribed within one square foot, divided into square inches. The spaces being numbered from right to left, and from top to bottom, the exact position of any disturbance observed could thus be easily ascertained and recorded. The above is a very powerful and convenient combination o1fering advantages l'lU'ely obt^ned, except by very costly in struments; for instance, to-day with a 36-in. achromatic, 6 inches in diameter, taking the image in its princ.pal focus as one, I threw an image of the sun on the screen, magnified ' 900 times, a faint spot appeared to be only one, but on increasing to 80,000 times it was resolved into five separate and distinct spots.. I know of no other combination that will give a like result so cheaply.jos. VOGLK. Tuscaloosa, Ala. «»«a> «. Steam Generators. Messrs. Editors :In your American Institute notice of my Steam Generator, on page 282, your remarks are correct so far as they go ; but permit me to add that the principle upon which this invention differs from all other attempts to. produce steam without having any water standing in the generator, is, that. the steam in the generator is made to let the water into it, and to graduate the quantity in the exact ratio demanded, so as to keep up any given supply and pressure requiredlimited only by the capacity of the generator. If SO pounds of steam be required, the overflow valve, on the water stream the pump is throwing, is set at that number of pounds, and when the pump is set in motion all the water it injects is immediately evaporated into steam, and as soon as it reaches, say, 51 pounds, it resists any more being fed into the generator, and passes back through the overflow valve into the tank, the resistance being the least in this direction. The steam now being used reduces the pressure, releasing the water in . the pipe so that it discharges just the amount of water necessary to keep up the supply demanded. Albany, N. Y.Thomas MITCHELL. The Fossil mau of Onondaga. Messrs. Editors :In your last issue I notice a letter written by Prof. Boynton in regard to this supposed antique man- image. It now seems that though Dr. Boynton was not humbugged into the belief that the stone was really a fossil, he made almost as ridiculous a mistake in his Jesuit theory. The image turns out to be the handiwork of a Canadian stone cutter named Geraud; who fancying himself a second Michael Angelo, “ fashioned an image in likeness uato a man,” but unluckily the artist died before achieving immortality. This is an age of speculation and parties “ on the make” saw a speculation in the eyes of poor Geraud's St. Paul. Ger- and had scarcely been himself buried, before his statue which he fashioned in secret, was spirited away and interred also in a spot judged fitting to carry out the plot of the fraudulent schemers. A year elapsed and poor Geraud was almost forgo'ten, while the one or two individuals to whom his secret had been confided had ceased to think either of him or his statue of St. Paul, when in digging a well'' or something of that sort, the feet of the entombed saint were discovered by the astonished ('.) diggers. Inch by inch the entire image was unearthed ; the speculators built there a tabernacle and reaped there large profits from a gullible public. It is said that they made more money in three days than they ever saw oeiore in all their lives, and certainly, as a joke, as well as a speculation this scheme is the best thing achieved since Barnum's palmiest days. Hereafter, it will be wise not to admit exhumed saints into good society until their antecedents have been well ascertained.G. B. Syracuse, N. Y. [There are contradictory reports about this matter. We were at first inclined to fdj pcse t;e ir atter a humbug, but we do not feel authorized to so pronounce it in the absence of further information.eds. The Prize Offered by the Swiss Government for a Time and Percussion Fuse. Messrs. Editors :In one of the late numbers of the Scientific American, I observe an inquiry by a correspondent relating to a certain prize offered by the Swiss Government for percussion fuses. They want what they term a “ universal fuse.” I send you an article bearing on the subject taken from the Newe Freie Presse, of Vienna, dated the 5th Oct., which conveys all the information that is required. Hanover, Germany.C. G. Mueller. ” The military department or tue Swiss Government has given notice, that it will pay a premium of 10,000 francs for a fuse which will possess the following qualitiesa full-sized model being required. The fuse must be a time and percussion fuse. The adjustment as to time should be managt'a ,le entirely by hand ; the time of burning should be at least ten seconds, and admit subdivisions of one half and one fourth seconds, the 'atter being also the time for the shortest adjustment. The fuse should be so constructed that it cm be made ready for firing only by uncovering and time adjustment ; the jarring motion ot the carriage should not be able to produce accidental ignition ; the fuse should be adaptable to the hollow projectiles which are used in the Swiss army. The construction should be sufficiently solid so that no premature discharge in the barrel can take place. The composition of the fulminate should be well enough protected against atmospheric influences, that after a number of years no material variation in.^he time of burning can be perceived The method of construction should not be laborious and expensive, and the corrrectneM of the process be easily regulated." Fresh-Water Wells near Salt Water. Messrs. Editors :In answer to your correspondent, J. Q. A nms, p'1go 263, current volume, I offer the folio vinlS explanation, : Tho sand is saturated with rain water which, not-. © 1869 SCIENTIFIC AMERICAN, INCWith standing the tides, will be intermixed with sea water very slowly, because the minute spaces between the sand prevent immediate mingling, and successive rain falls will repel the slowly advancing sea water before it reaches the well. Therefore at a certain distance from the shore the sand is always saturated with fresh watt r which can be obtained and used in the manner described by your correspondent.Hugo BiLGBRAM. Philadelphia, Pa. Fire from Steam Pipes. MESSRS. Editors :About twelve years ago, when in charge of a pattern shop in New York city, I had a steam glue heater for the use of the shop. and, having noticed a pine block lying upon it for several days, I picked it up to throw it away, but noticed it was partly charred through. It excited my curiosity, and I decided to replace it and watch it ; but after watching it, and having the night watchman look after it nights for about a month I gave it up. By that time it was completely charred through, not like a piece of charcoal from a pit or kiln, for it had a dark-brown color, but would ignite an i burn as easily as a piece of charcoal made from the sime kind of wood. I have since always been careful in putting in steam pipes to keep the pipes from coming in contact with the wood work. With clean wood, I think there is little danger ; but with wood containing considerable pitch, or saturated with oil, I think danger from spontaneous combustion is imminent. Though requiring care in putting up, I consider steam pipes the safest and most economical means of heating a factory, storfe, or dwelling, and have advocated their use in different ways during ten years of engineering practice. Marquette, Mich.A SUBSCRIBER.