394 Prof. A. De la Rive's Researches on the Magnetic 



The present memoir consists of five sections. 



In the first I describe the apparatus and the experimental 

 processes I have used. 



In the second I give the results furnished by experiment in 

 operating upon a certain number of liquids very different one 

 from another. 



In the third I study the influence of variation of temperature 

 on the magnetic rotatory polarization of liquids. 



In the fourth I endeavour to determine the ratio which exists 

 between the magnetic rotatory power of a mixture of two liquids 

 and those of the ingredients of which the mixture consists. 



In the fifth I exhibit the result of the experiments I have made 

 upon the magnetic rotatory power of some isomeric liquids. 



§ 1. Description of the Apparatus and the Experimental 

 Processes. 



The electromagnet which I used is composed of two cylinders 

 of soft iron of 12 centims. diameter and 36 centims. long, each 

 with a cylindrical perforation through its axis 3 centims. in dia- 

 meter, and the two wrapped round with 1665^- metres of insu- 

 lated copper wire of 2*7 millims. diameter and the total weight 

 of 92^ kilogrammes. The wire encircling one of the cylinders 

 is 835 '8 metres long, and makes 1555 turns, forming 16 super- 

 posed layers ; the other is 829*7 metres long, and makes 1537 

 turns, forming also 16 superposed layers. The two cylinders of 

 soft iron, thus enveloped, are arranged opposite to each other on 

 a cast-iron stand, so that their axes are in the same horizontal 

 line. A screw, moved by a crank, brings into contact the two 

 interior polar surfaces, or separates them to a maximum distance 

 of 30 centims. A prismatic bar of soft iron, terminated by two 

 shorter bars perpendicular to it, which are 10 centims. wide and 

 3 centims. thick, serves as an armature connecting the extremi- 

 ties or exterior polar surfaces of the two cylinders. It can slide 

 in such a manner as not to hinder the approach or separation of 

 the interior polar surfaces*. Strong pressure-screws keep in 

 place, at the desired distance, the two cylinders, which, without 

 this precaution, would be liable to rush together at the moment 

 of magnetization and to break the objects placed between the 

 polar surfaces. 



For the experiments on rotatory polarization, on the side near- 

 est to the source of light a NicoPs prism is fitted to the opening 

 of the perforation of the nearest cylinder, to serve as polarizer ; 

 a similar analyzing-prism is placed at the extremity of the per- 

 foration of the other cylinder of soft iron. This extremity is 



* The addition of this armature augments the force of the electromagnet 

 in the ratio of 3 : 2. 



