BURNING-GLASS. 



fii jufliiication of tlie opinion we have given, we now pro- 

 ceed to I'tibiiiit a felcAed enumrralion of the experiments 

 wliicli were made witli this julHy celebrated inftrurrent, 

 uuJcr tlie iiifpeclion of maior Gardner, brother to the admiral 

 li-rd Gardner, together with fome gentknicn of the Royal 

 Socictv. 



■Subdanees fnfed, with their Weight and Time 

 of I'lifion. 



Gold, pure, 



Silver, do. 



Copper, do. 



Platina, do. 



N'ickell, 



liar Jroii, a Cube, 



Call Iron, a Cube, 



Steel, a Cube, 



Scoria of Wrougiit Iron, 



Kearlh, 



Cauk, or Terra Ponderofa, 



A Topaz, or Chryfolite, 



An Oriental Emerald, 



Cry Hal Pebble, 



Topaz, 



Flint Oriental, 



Rough Cornelian, 



Jafper, 



Onyx, 



Garnet, 



White Rhomboidal Spar, 



Zeolites, 



Rotten Stone, 



Common Slate, 



Albedos, 



Common Lime Stone, 



Pumice Stone, 



Lava, 



Volcanic Clay, 



Cornifh Moor Stone, 



Mr. Parker farther informs ns, that a diamond, weighing 

 10 grains, cxpofed to this lens for ;o minutes, was reduced 

 to 6 grains ; during which operation it opened, and foliated 

 like the leaves of a flower, and emitted whitilli fumes, and 

 when clofed again it bore a polifli, and retained its form. 

 The editor has been favoured by Mr. Parker Jun. with the 

 ■following additional obfcrvations on the powers of this 

 lens. 



Gold remained in its metallic ftate, without apparent 

 diminution, notwithftanding an expofure at intervals of 

 many hours : but what is remarkable, the reft, or cupel, 

 which was com.pufed.cf bone a(h, was tin£lured with a 

 beautiful pink colour. 



Platina. The experiments evince that the fpecimens were 

 in different ftates of approach to a complete metallic form ; 

 feveral of them threw off their parts in fparks, which in moft 

 inllances were metallic. 



Copper, after three minutes expofure, was not found to 

 have loll in weight. 



Iron, fleel-lhear. What is remarkable in this experiment is, 

 that the lower part, i. e. that part in contaft with the char- 

 coal, was firlt melted, when that part which was expofed to 

 the focus remained uufufcd : an evidence of the effed of flux 

 cQ this metaL 



Iron fcoria, and tl>e turnings of iron. The fcoria appears 

 to have been me'Kd in much lefs time than the turnings, 

 a refult that might have been expefted to have been direttly 

 the reverfe ; but fome allowance mull be made for the 

 probable difference in the effefls or iKteniities of the folar 

 rays at the periods at which the experiments were matle. 



Calx of iron from vitriolic acid, precipitated by mild 

 fixed alkali, weighing 5 grains before expofure, weighed 

 afterwards 5^ grains ; which indicates an increafe of weight 

 by an abforption of phlogillnn. 



Regulus of zinc began alinoll inftantly to flow, and wa* 

 nearly evaporated ; the remains were magnetic. 



Regulus of cobalt was completely evaporated in ^57". 



Regnkis of bifmuth was nearly evaporated when expofed 

 on a charcoal reil ; but on black lead it began to fufe in 2", 

 and very foon after pafTed into a ftate of complete tnfion ; it 

 loll only half a grain in weight from an expofure of 180" ; 

 on a boneafh rell it fufed in 3", and in iSo" it was reduced 

 to 7s grains. 



Regulus of antimony : 3^ grains were fnfed in 3'' on 

 charcoal, and after 195" there remained only 11 grains; 

 but when expofed on a charcoal rell for the fame time, 

 there remained afterwards zS grains, which fliewed a mag- 

 netic aflfeflion. 



Fine kearlh from the cannon foundery cv .^orated very 

 faft during 120", and in 30" more the remainder began to 

 flow into globules, which, on being cold, were attracted by 

 the magnet. This experiment of ilfelf fupports the claim 

 of this inftrument to a vaft fuperiority over the heat of any 

 furnace hitheito known. 



Cryftal pebble of North America : 5 grains cxpofed con- 

 traded in 15", pcrfedlly glazed in 135", tbuUefced in Ijo', 

 and when taken out appeared femi-diaphanous, of a flatc 

 colour. 



Several of the femi-cryftaUine fubftances, expofed to the 

 focal heat, exhibited fymptoms of fufion : fuch as the agate, 

 oriental flint, cornelian, and jalper ; but as the probability is 

 that tliefe fubftances were not capable of complete vitrifica- 

 tion, it is enough that they were rendered externally of a 

 glaffy form. 



Garnet completely fufed on black lead in 1:0", loft 

 •J of a grain, became darker in colour, and was attrafted by 

 the magnet. 



Ten cut garnets taken from a bracelet, began to run the 

 one into the other, in a few feconds, and at lall formed into 

 one globular garnet. 



The clay ufed by Mr. Wedgwood to make his pvro- 

 metric left, run in a few feconds mto a white enamel. .Seven 

 other kinds of clay fent by Mr. Wedgwood were all 

 vitrified. 



Several experiments were made on limeftone, fome of 

 which were vitrified, but all of which were agglutinated ; 

 it is, however, fufpeftcd that fome extraneous fubftance 

 muft have been intermixed. A globule produced from one 

 of the fpecimens, on being put into the mouth, flew into a 

 thoufand pieces, occafioned, it is prefumed, by the raoif- 

 ture. 



Stalaftites Zeolithus fpatofus : 9 grains took a globular 

 form in 60"; in 148" the globule began to get clear ; in 

 155" was perfeAly tranfparcnt, and as it grew cold di- 

 minifhed in tranfparency, and at lall refoKed itfelf into a 

 beautiful red ; on being cut by a lapidaiy, it was found 

 to be fo hard as to ferve as a diamond to write on glafs. 



Several fpecimens of lavas, and other volcanic produc- 

 tions, were expofed to the focus of the lens, all of which 

 yielded to its power. This furnace of nature, the volcano, 

 is fuppofed to be hotter than any furnace conftrufted by the 



art 



