It must be recollected by those who have bad an opportunity of examining the effects of this lens, that the external part of the focal light was less intense than that part which was near the centre of it; or rather, that the effect was very much accumulated in the centre but as it is possible that the refraction of the light and of the caloric fluid may not take place in the same angles, we think it safest to consider it as of an uniform effect, and after deducting one-fourth part thereof as a compensation, there remains 55454°, as the expression of its power. As the application of the second lens reduced the diameter of the focus to half an inch, the effect, without allowing for the reduc tion of its power, would be equal to 221816°, but deducting one-fourth for the second transmission, there remains 166362°, as the expression of its power.
Mr. Parker farther informs us that a tliamond, weighing 10 grains, exposed to this lens for was reduced to 6 grains ; during which operation it open ed, and foliated like the leaves of a flower, and emitted whitish fumes, and when closed again it bore a polish, and retained its form. Gold remained in its metallic state without apparent diminution, not withstanding an exposure at intervals of many hours : but what is remarkable, the rest, or cupel, which was composed of bone-ash, was tinctured with a beautiful pink colour.
The experiments on platina evince that the specimens were in different states of approach to a complete metallic form ; several of them threw off their parts in sparks, which, in most instances, were metallic. Copper, after three minutes exposure, was not found to have lost in weight.
What is remarkable with regard to ex periments on iron is, that the lower part, is e. that part in contact with the charcoal, was first melted, when that part which was exposed to the focus remained nn fused : an evidence of the effect of flux on this metal.
Several of the semi-crystalline substan ces, exposdd to the focal heat, exhibited symptoms of fusion : such as the agate, oriental flint, cornelian, and jasper; hut as the probability is that these substances were not capable of complete vitrification, it is enough that they were rendered ex ternally of a glassy form. Garnet com pletely fused on black-lead, in 121' lost ith of a grain, became darker in colour, and was attracted by the magnet. Ten cut garnets, taken from a bracelet, began to run the one into the other in a few se conds, and at last formed into one globu4 lar garnet. The clay used by Mr. Wedg wood to make his pyrometric test run in a few seconds into a white enamel. Seven other kinds of clay sent by Mr. Wedg wood were all vitrified. Several experi ments were made on lime-stone, some of which were vitrified, but all of which were agglutinated ; it is, however, suspected that some extraneous substance must have been intermixed. A globule pro duced from one of the specimens, on being put into the mouth, flew into a thousand pieces, occasioned, it is presum ed, by the moisture.
Some experiments were made in the year 1802, with Mr. Parker's lens, with the view of ascertaining whether the moon communicated any heat to the earth, in common with the reflected light from which we derive so much advantage. This experiment was attended by Sir Jo. seph Banks, with several members of the Royal Society, together with Dr. Craw ford, who provided the most sensible thermometers ; but after applying them to the luminous focus, so far from a perceptible increase of heat, it was thought there was perceived rather a di minution thereof; but this suspicion did not lead them to a fair investigation of the fact. Since this period some experi
ments have been made, that evince the power of communicating cold by reflec tion ; but as this fact has not yet been ex plained consistently with the present re ceived theory, we shall content ourselves withtakingnotice of the experiment made by M. Pictet. Two concave mirrors being placed at the distance of 10j feet from each other, a very delicate air thermome ter was put into one of the foci, and a glass matrass fill of snow in the other. The thermometer sunk several degrees, and rose again when the matrass was re moved. When nitric acid was poured upon the snow (which increased the cold) the thermometer sunk 5° or 6. lower. Here cold seems to have been emitted by the snow, and reflected by the mirrors to the thermometer, which it is thought could not happen unless cold were a substance. It has been found, that upon an admixture of equal quanti ties of snow, which is always at 32°, and of water heated to 172°, the result is, that the compound only retains the lowest heat of 32°, so that 140° of heat or calo ric disappears. Much has been said re specting the point or degree at which the thermometer should indicate the pre sence of heat. The experiments of Dr. Crawford seem to place it at 1268° below the present 0 ; Mr. Kirwan places it at 1048°; Messrs. Lavoisier and La Place at 2Y36°; and by a mixture of four parts of sulphuric acid with three pints of water, it seems that it should be placed at 5803° below 0. Experiments of this kind may be made ad infinitum, and in time it may possibly be ascertained that cold is a real substance; but for the purpose of get ting an answer to the present question, we will accommodate the scale of Fah renheit, by adding 108° thereto, so as to make the 0 correspond with the caloric imbibed by snow or ice before it can melt.
The superficies of spherical bodies are to each other as the squares of their re spective diameters. The diameter of the moon is considered to be 2180 miles, and its mean distance from the earth 240,000 ; from which it follows, on the supposition that all the solar rays received by the moon were reflected back, and that the earth was absolutely without heat, that the effect of this reflection would be found to be .00367 of a degree (for 240,000X 2 2180° :.00367); which multiplied into 1056.25, and this sum in creased four timesfor the increased power of the second lens, would give 15.51234° as the heat of the focus ; 98.28766° be low the present 0, or 124.28766° below the freezing point. This dissertation is interesting in another point of view, for this calculation ascertains that the light afforded by the moon, when compared with that by the sun, abstracting all im pediments in both cases, is only as 1 to 48480.
Asubscription was proposed for raising the sum of 700 guineas towards indemni fying the charges of the inventor, and re taming the very curious and useful ma chine above described in our own coiin try ; but from the failure of the subscrip tion, and some other concurring circum stances, Mr. Parker was induced to dis pose of it to Capt. Mackintosh, who ac companied Lord Macartney in the embas sy to China ; and it was left, much to the regret of philogophers in Europe, at Pe kin; where it remains in the hands of persons, who most probably know neither its value nor use.
BuRNING-mountains, the same with canoes. See VoLcAno.