85 



being as cause and effect of the healthy operation of this basic system 

 of the animal oeconomy. And as it is not essential to the motions of 

 the iris, either to their performance or that they be understood, that 

 they partake of any of those peculiarities, the distinguishing fea- 

 tures of muscular tissue, and as we find that this membrane is 

 obedient to those laws which are applicable to each organ under 

 immediate sympathetic influence, and opposed to those phenomena 

 which result from spinal and 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 these 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 

 is contracted, to produce, in proportion to its contraction, convexity 

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

 bers, these processes fall down to form a serrated border upon the lens. 



7. " On the Automatic Temperature-compensation of the Force 

 Magnetometers." By C. Brooke, M.B., F.R.S. Received May 8, 1851. 



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 at 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 difference 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 coefficient. 



In the balanced magnetometer the compensation is effected by 



