142 



BURNING INSTRUMENTS. 



Burning 

 Instru- 

 ments. 



3 of an inch, and the weight of the lens 21 pounds. 

 The corpbined focal length of these lenses is 5 feet 3 

 inches, and the diameter of the focus half an inch. These 

 lenses are placed at the extremities of a truncated co- 

 nical frame, consisting of twelve ribs of wood. Near the 

 smaller end B is fixed a rack D, which passes through 

 the pillar L, and is moveable by means of a pinion 

 within the pillar, driven by the handle E. A bar of 

 wood F, fixed at G between the two lower ribs of 

 the cone, carries an apparatus H, which turns on an 

 universal joint at K, and also moves to or from F in 

 a chased mortice. This apparatus, which carries the 

 iron plate I for holding the substances to be examined, 

 may thus be placed exactly in the focus of the lens B. 

 The conical framing is supported by pivots upon a 

 strong iron bow AC, which rests upon a mahogany 

 frame LL, with three feet MMM furnished with cas- 

 tors. Friction wheels are placed under the table N, 

 to facilitate the horizontal motion. 



The following experiments with this lens were 

 made in the presence of Major Gardner, and of se- 

 veral members of the Royal Society. 



Experi- Substances fused, with their Weight in Time in 



merits with weight and time of fusion. grains. seconds. 



Parker's Common slate, 10 2 



k ns> Scoria of wrought iron, . . 12 



Gold, pure, . , 20 3 



Platina, do 10 3 



Nickel, ; 16 



Cast iron, a cube, .... 10 3 



Silver, pure, 20 4 



Crystal pebble, 7 



Terra ponderosa, or barytes, 10 7 



Lava, 10 7 



Asbestos, 10 10 



Steel, a cube, 10 12 



Bar iron, do 10 12 



Garnet 10 17 



Copper, pure, 33 20 



Onyx, 10 20 



Zeolites, . 10 23 



Pumice stone, 10 24- 



An oriental emerald, ... 2 25 



Jasper, 10 25 



White agate, 10 30 



Flint, oriental, 10 30 



A topaz or chrysolite, . . 3 4-5 



Common lime- stone, ... 10 55 



Volcanic clay, 10 60 



Cornish moor stone, ... 10 60 



White rhomboidal spar, 10 60 



Rough cornelian, .... 10 75 



Rotten stone, 10 80 



A diamond of 10 grains, when exposed to the lens 

 for 30 minutes, was reduced to 6 grains. It opened, 

 foliated, and emitted whitish fumes, and when again 

 closed, it bore a polish, and kept its form. 



Gold retained its metallic state, though exposed 

 for many hours. 



The specimens of platina were in different states of 

 approach to a metallic form. 



Copper did not lose any of its weight after an ex- 

 posure of three minutes. 



Iron steel shear melted fjrst at the part in contact 



with the charcoal, while the other part exposed to 

 the focus was un fused. 



Iron scoria melted in much less tim^ than the turn- , 

 ings of iron. 



Calx of iron from vitriolic acid, precipitated ' by 

 mild fixed alkali, weighed 5 grains before exposure, 

 and 5^ after it. 



The remains of regulus of zinc, after it had melted 

 and was nearly evaporated, were magnetic. 



Regulusof cobalt was completely evaporated in 57". 



Regulus of bismuth, exposed in charcoal, was near- 

 ly evaporated : in black lead it began to melt in 2", 

 and was soon after completely fused : Iron, on expo- 

 sure of 180", lost only half a grain; when placed 

 on bone ash, it fused in 3". 



Regulus of antimony, 33 grains, on charcoal, were 

 fused in 3", and 11 grains only remained after 195". 



Fine kearsh from the cannon foundery evaporated 

 very fast during 120", and 30" afterwards, the re- 

 mainder flowed in globules, which were attracted by 

 the magnet when cold. 



Crystal pebble of North America, five grains, 

 contracted in 15", were perfectly glazed in 135", 

 ebullesced in 150", and became of a slate colour, and 

 semitransparent. 



Agate, oriental flint, cornelian, and jasper, were 

 rendered externally of a glossy form. 



Garnet, placed upon black lead fused in 120". It 

 became of a darker hue, lost one- fourth of a grain, 

 and was attracted by the magnet. Ten cut garnets 

 from a bracelet run into one another in a few seconds. 



Mr Wedgewood's pyrometrical clay run into a 

 white enamel in a few seconds. Other seven kinds 

 of clay sent by that gentleman were vitrified. 



Limestone was sometimes vitrified and sometimes 

 agglutinated. A globule from one of the specimens 

 flew into a thousand pieces when put into the mouth. 



Stalactites zeolithus spatosus, nine grains, took a 

 globular form in 60". The globule began to become 

 clear in 148". It became perfectly transparent in 

 155". When cold, its transparency diminished, and 

 it assumed a beautiful red colour. 



Lavas and other volcanic products likewise yielded 

 to the power of this lens. 



In the year 1802, Sir Joseph Banks, Dr Crawford, 

 and some other members of the Royal Society, were 

 present at an experiment for concentrating the lunar 

 rays ; but though the most sensible thermometers 

 were applied, it was rather thought that there was a 

 diminution than an increase of heat. 



It was not to be expected that this powerful lens, 

 which cost such a large sum of money, could have 

 been retained in the hands of Mr Parker. That in- 

 genious artist was naturally desirous to indemnify 

 himself for the expense of its construction. A sub- 

 scription was therefore opened for purchasing the 

 lens, as a national instrument ; but, to the disgrace of 

 our country, this subscription completely failed, and 

 Mr Parker was induced to sell it to Captain Mackin-! 

 tosh, who accompanied Lord Macartney to China. 

 This valuable instrument was left at Pekin, where it 

 remains a monument of Chinese ignorance, and Bri- 

 tish parsimony. 



From the history which we have now given of diop-, 

 trie burning instruments, it evidently appears, that irt 

 every construction which has yet been proposed, a 



