pands and flies off by heat; then, becomes so much less. of course the clay, He next explained the method of compensation for pendulums and springs of watches, which is fully described in Dr. Lardner (Vol. xxxix. Cab. Cyc. chap. ii.). He then entered upon the dilatation of liquids and gases, and described the instrument of Dulong and Petit. He then described the construction of thermometers, much in the same way as is done by Dr. Lardner (Cab. Cyc. art. Heat, chap. v.). He shewed, also, that mercury, as having the greatest range, is most useful in common thermometers; according to Cavendish, it freezes at about 39° below zero-and boils at 666°, according to Dalton. He also described the differential thermometer of Leslie, of which he exhibited a model. 8 The part of the lecture on which he now entered, was new to me, as I had not then read that part of "Lardner on Heat," which relates to radiation, reflection, and absorption. While intent upon the lecture, I was suddenly disturbed F. J. P. Dr. Dalton, the first LL.D. in the society of Friends. by a blast upon my face, which seemed hot as the Simoom itself. Wondering from whence it came, not knowing whether it proceeded from the tail of a salamander, or the nose of Phalaris's bull, my eye happened to catch sight of a man pacing with a pail towards the platform, in which I had a glimpse of a large red-hot iron ball, quietly reposing in a mass of heated sand. The following diagram may serve to explain the experiments that followed. A B are two large reflectors placed at each end of the platform C E; D is a large ball heated very hot, and placed on a stand in the focus of the mirror. The reflected heat produced a great effect on the differential thermometer at F, and even ignited a piece of phosphorus. If the rays are intercepted by a plate of glass, no effect is produced. 1833, 10 mo. 18th.-At a preliminary meeting of the chemical class, in the evening, the lecturer a member of the class-began by stating the advantages of chemistry, and its uses in geology, botany, &c. He proved, by experiment, two properties of matter, of great use to the chemist. 1st, Its porosity, or the dilatation of matter by heat; that is, when heat is applied to a body, its particles remove themselves from each other, and the body dilates and becomes more porous. This expansion he proved by heating a hammer, and then applying it to a slit which it just fitted when cold, but which it would not now enter. 2d, Its divisibility. He filled a glass jar with water, into which he put a grain of muriate of soda (common salt), and the single grain was diffused throughout the whole of the water. He proved this by shaking the water well, emptying part of it into a glass, and then introducing a test of salt. The moment he emptied this test into the glass, the water, which before appeared clear, looked quite thick, of an opaque white colour. 10 mo. 25th. Account of a Meeting of the Chemical Class. The meetings of our class continue to be inter esting; and it may not be unprofitable to give a short account of the leading subjects of our inquiry. At our second meeting, the lecturer continued his address. After that is finished, the members of the class may ask any questions, or call for any explanations they think proper. The table was plentifully covered with bottles; and I observed at one end a small pneumatic trough. On a large card were written the names of the chief bodies known in chemistry, arranged according to the plan of Dr. Turner, whose work is the text-book of the class. Dr. T. makes two grand divisions-non-metallic and metallic, which are further divided into classes. Oxygen is a simple substance, which is almost universally diffused. Naphtha, it was said, is one of the very few known substances which does not contain it. Oxygen may be obtained from the oxide of manganese, from saltpetre (but in this case it is apt to be mixed with azote, if great care is not used), and from an artificial compound chlorate of potash, from which it may be best obtained. We made the beautiful experiment of burning of charcoal in oxygen: the receiver was filled with beautiful scintillations. The lecturer made use of a precaution against bursting the jar, which I do not remember to have seen employed before; viz. affixing a flaccid bladder to the neck of the bottle or to the cork; so as to communicate with the inside, and form a vent, in case of any great expansion of the oxygen. All of a sudden, when the bottle appeared full of sparks, the bladder became filled, and, not being very strong, it burst. The result of this combustion, carbonic acid gas, immediately extinguished a lighted taper plunged into it. The next gas which we examined was chlorine, which, it is said, by daylight is of a yellow colour; but, by lamplight, it appeared a transparent white. Some copper filings placed in it, burnt with a reddish kind of flame. The result was a greenish looking liquid at the bottom of the jar, which I suppose is called chloride of copper. Hydrogen, it is said, does not keep; we, therefore, made some for immediate use. I do not know from what it was obtained. Another mem ber of the class, who made it, put something into a bottle with a wide mouth, having a bent tube in the cork, which was placed in the pneumatic S |