quinine sulphate, whilst another was exposed to the full action of the unshaded light. The times of exposure varied between one and ten minutes. The intensity of the actinism was measured by Roscoe's method, which need not be described. The curve obtained from the paper exposed behind the quinine cell is practically identical with that obtained optically from the blue components when any one point in the former curve is made to correspond to a point in the latter which has the same abscissa. The following Table gives the results of the experiments made with this particular machine. The numbers or letters in the first column refer to the numbers in the diagram. The horsepower given is the total horse-power recorded less that required to drive the machine with the brushes up. *A? is placed against the 600 revolutions, as the engine at that velocity worked somewhat unequally. The following is a statement, furnished me by Captain R. Y. Armstrong, R.E., of the electrical conditions of the circuit. The resistance of the stationary wire 4:46 ohms. = magnetizing coil = 0.44 ohm. In the generator the resistance of the light-circuit coil = 0.24 ohm. The light coils were in divided circuit, as were also the right and left stationary coils. When driven at from 375 to 383 revolutions, the resistance of the voltaic arc was about 0.18 ohm; the other resistances in the circuit were 0.7 ohm. The electromotive force of the machine when driven at the above speed was 111 volts, a measure which has been arrived at by Captain Armstrong from other experiments. The electromotive force between 375 and 383 revolutions of the armature was assumed to vary as the number of revolutions, an assumption which was borne out as practically correct by other measurements made for the purpose. In order to ascertain what effect the insertion of resistance had on the current, the following experiment was undertaken by Captain Armstrong with a smaller form of gramme machine, called Machine No. II. Two resistances were inserted in the circuit for two different sets of readings, in the first case 1·1 ohm of total resistance, in the other 2.72. Table VI refers to these experiments, the curve marked A in the Diagram V being that due to the first, B being that due to the second. It will be noticed that practically the curve becomes a straight line, or, in other words, the electromotive force increases directly as the number of revolutions of the armature, a result which might have been expected theoretically. It will also be seen that the current for any given number of revolutions varies inversely as the resistance in circuit, or, in other words, that the electromotive force for a given number of revolutions is constant. In any results, therefore, which are given descriptive of the light produced by any machine, the following should be noted: Number of revolutions of armature; Resistance in circuit; Horse-power expended; Colour of light measured; Electromotive forces. together with the size of the carbons employed, and other obvious details. II. "Experimental Researches on the Temperature of the Head." By J. S. LOMBARD, M.D., formerly Assistant-Professor of Physiology in Harvard University, U.S. Communicated by H. CHARLTON BASTIAN, M.D., F.R.S., Professor of Pathological Anatomy in University College, London. (Abstract.) The present communication forms an abstract of the first portion of a series of investigations having the following primary objects in view : 1st. To find out, as far as possible, the normal relative temperatures of different portions of the surface of the head, when the brain is comparatively inactive. 2nd. To study the effect of different mental states upon the different portions of the surface of the head previously examined in the condition of comparative cerebral inactivity. The ultimate objects were two-fold; namely :— 1st. To furnish, if possible, some reliable data as a starting point |