The subject of the paper was discussed, and a special committee, consisting of Mr. Hogan, Mr. Bingham, Mr. Barnes, Prof. Cooley, and Mr. Colvin, were appointed by the chair to report at a special meeting to be held on Tuesday evening, the 27th inst., at the rooms of the Insti

tute.

A New Form of Rotator. By LEROY C. COOLEY, PH. D.

[Read before the Albany Institute, April 1, 1873].

Rotary motion is of vital importance as a means of developing principles in physics Optical, electrical, acoustic and magnetic experiments, to say nothing of the numerous well known illustrations of the "Central forces" constitute a series of important demonstrations of great beauty and variety. Until the present, no instrument has had capacity to grasp the necessary conditions of all cases, and consequently various forms of whirling table or rotator, each adapted to special experiments, have been devised.

But notwithstanding their great variety the experiments in rotary motion may, for the most part, be grouped in three classes, viz: First, those in which the rotating body must be firmly attached to a vertical axis: second, those in which the rotating body must be freely suspended from a vertical axis, and third, those like the Geisler tubes and optical disks, in which the rotating body must be firmly attached to a horizontal axis.

To adapt a single instrument to these three classes of experiment, it is only necessary to utilize both ends of the axis of the pulley and to be able at a moment's notice to shift the axis itself from a vertical to a horizontal position.

This has been accomplished as follows:- From the centre of a base of convenient size a single column rises to a height of about two feet. Across the top of this column, and firmly fixed upon it, is a table measuring about twenty inches in length by five in width. Upon this table and fastened to it by hinges is a strong bar of wood, two and

a half inches square by about three feet in length. This bar carries the driving-wheel and pulley by which the motion is obtained. The steel shaft of the pulley passes through the bar and is furnished with a screw at each end. By this means articles may be firmly attached to a vertical axis projecting either upward or downward as may be most desirable. A hook accompanies the

lower end of the shaft from which bodies may be freely suspended. The bar carrying the driving wheel and pulley, being hinged upon the table, is held firmly in place by a catch. By sliding this catch, the bar turns upon its hinges, carrying the wheel and pulley with it, and thus throws the shaft into a horizontal position, instantly adapting it to receive attachments for optical disks, Geisler tubes or other pieces which must rotate in a vertical plane.

It does not seem that this rotator needs to be essentially more costly than the old style of whirling table; that it has capacity to receive attachments for all varieties of rotary motion in illustrating the different departments of physics would seem to make it more desirable than any hitherto devised.

Detection of Heat by Convection. By L. C. COOLEY, PH. D.

[Read before the Albany Institute, April 1, 1873.]

In the course of a series of experiments on certain electrical actions, the electroscope in use, which was one of Coulomb's form, gave some anomalous and unexpected results. Its needle would respond with great promptness to the attraction of all the usual electrics, but what was, for a moment, a little puzzling, was the fact that it would swing with equal alacrity whenever such good conductors as iron and copper, after gentle friction, even while held in the hand, were brought into its vicinity. Evidently under such circumstances the motion of the needle could not be due to any electrical action: it was quickly seen to be caused by the gentle rise of temperature in the solid rubbed. So gently warmed by friction the metals became centres of disturbance in the air. The cooler portions around flowed toward the heated centre to take the place of the lighter air pushed upward. The pith ball of the electroscope, caught in these delicate currents, was wafted toward the body introduced. Its motion, therefore, declared the presence of the heat.

Can this principle be applied in the construction of thermoscopes? As one step toward answering this question, a very slender glass tube, five or six inches long, weighing a few grains only, was suspended by a single fibre of silk, about a foot in length, attached so as to balance it in a horizontal position and hung within a glass case to protect it from air currents. An opening was left in the cover for the introduction of the body to be tested and a

graduated scale was placed under the needle to measure the motion produced.

With this arrangement some very encouraging results have been obtained. The following examples will serve to illustrate: The end of an iron wire after an almost momentary pressure between the fingers, held near the needle, quickly drew it out of place. A hammer falling by its own weight through a distance of 15 inches and striking upon the end of the wire, evolved so much heat that the needle was wafted through an arc of 60°. A small glass tube gently rapped upon the edge of the table and then placed inside the instrument gave motion to the needle, distinctly seen by the most distant member of a large class.

Next to the expensive Thermo-pile this Convection Thermoscope is probably the most delicate indicator of heat at present known.