1^! UifyuL Society . 



whicJi result from spinal auU cerebral influence, it may be asserted 

 that the contractility of the iris is, primo loco, the motor power of 

 the sympathetic. For the iris is an irritable membrane with power 

 alone of involuntary motion and tension, its active condition agreeing 

 in tiiesG respects with vegetative life in general. And as animal 

 death may be said to ensue when deep sleep takes possession of the 

 senses, when those systems under spinal and cerebral influence are 

 rendered inactive, to be fitted for renewed exertion on waking, it 

 follows, that those organs which still remain active cannot be go- 

 verned on the same principle, but must necessarily be subject to the 

 sole remaining power, through which is accorded involuntary mo- 

 tion, motion which never tires, and tension its active condition. 

 . The fimbriated edge of the ciliary body floats loosely in the poste- 

 rior chamber around the lens, to produce, through the to and fro 

 motion of each process (their aggregate number representing a 

 circle), a current forwards or towards the iris. The force of this 

 current is in a ratio to the pupillary opening, being increased as this 

 b contracted, to produce, iu proportion to its contraction, convexity 

 of the iris. On the escape of the aqueous humour from the cham- 

 bers, these |)rocesses fall down to form a serrated border upon the 

 lens. 



6. *' On the Automatic Temperature-compensation of the Force 

 Magnetometers." By C. Brooke, M.B., F.R.S. 



After explaining the necessity of automatic temperature-compen- 

 sation in these instruments in order to give the highest degree of 

 accuracy to results deduced from the ordinates of the magnetic 

 curves, the author infers from a reference to the formula expressing 

 the conditions of equilibrium of the bifilar magnet, that the interval 

 between the lower extremity of the suspension lines will be most 

 advantageously submitted to some mechanical agency governed by 

 change of temperature. 



The object in view has been attained by attaching the lower ends 

 of the suspension skein to the adjacent ends of two zinc tubes that 

 are clamped to a glass rod which is attached by its middle point to 

 the middle of the bar-magnet. When the temperature rises, the 

 ends of the skein will evidently be approximated to each other by a 

 quantity that is equal to the diflT?rencc of expansion of the lengths 

 of zinc and glass intervening between the clamps. The interval 

 between the clamps is to be approximately determined by calcula- 

 tion, and corrected by experiment, so that the ratio of the expansion 

 to the distance between the threads may be equal to the first term 

 of the temperature coeflScient. 



In the balanced magnetometer the compensation is effected by 

 means of a small thermomettr attached to the magnet, the stem of 

 which is parallel to the axis of the bar. In this thermometer, the 

 size of the bulb, its distance from the freezing-point and length of 

 the scale, nmy be so proportioned to each other, that the second as 

 well as the first term of the temperature coefficient yf^^^l •^. Repre- 

 sented in the correction. 



