92 
POPULAR SCIENCE REVIEW. 
Rotatory Magnetic Polarization in Oases forms the subject of along paper 
in the Annales de Chimie etde Physique, by M. H. Becquerel. The principle 
has already been described. In the present paper a minute account is given 
of the apparatus employed, and the precautions adopted to insure accuracy. 
The apparatus consists of two distinct parts, (1) the optical, (2) the mag- 
netic. The gas was contained in a tube 3 *27 metres long, closed by parallel 
glass ends. Around, but not touching, this are six large coils, each contain- 
ing 15 kilogrammes of wire, or about 90 kilogrammes in all, with a length of 
1380 m., when joined in a continuous series. The current used was from 80 
nitric acid batteries of large size, in two series of 40 each. Under so powerful 
a current, the conductors and the tube itself soon became warm, rising to a 
temperature of 40° Centig. or 102° Fahr. To estimate variations in the cur- 
rent from this cause, and also from changes in the battery, a sine-galvano- 
meter was placed in a shunt from the main circuit, and a curve plotted from 
its indications. The quantity of gas operated on amounted to about 37 litres. 
It acted of itself as an air-thermometer by means of a pressure-tube. The 
amount of rotation being very small, only about 5' of angular measure with 
an inverted current, it was found expedient to amplify it by the method of 
reflection used by Faraday and Foucault. Magnetic rotation is known to be 
proportional to the path traversed, in whatever direction it may pass. The 
source of light was lime, passed, in some instances, through coloured dia- 
phragms. The polarizer was a large Nicol’s prism, giving a beam over an 
inch in diameter. By means of two plane mirrors silvered in their middle 
part, the ray to be polarized was passed three, five, seven, or nine times 
along the length of the tube before being received on the analyzer. This 
consisted of a Foucault’s prism mounted on a divided circle with a vernier 
reading to minutes of arc. Four double reflections, with nine passages of the 
ray through the tube, were generally employed. The current being passed 
in one direction the two images were brought to similar tint ; and the current 
being then reversed, the analyzer was turned to similarity, and the angle read 
off, giving double the magnetic rotation for the substance experimented on. 
The necessary corrections for various causes of error were referred to bisul- 
phide of carbon, the rotatory power of which is large. Besides temperature 
and magnetic intensity named above, there were, the displacement and want 
of homogeneousness in the source of light, rotations caused by the glasses, 
lenses, and mirrors of the apparatus, — all these are discussed at length and 
tabulated. A remarkable relation is shown between the index of refraction 
of a gas and its power of magnetic rotation. Oxygen, however, forms a 
notable exception. 
ZOOLOGY. 
A New Form of Cystic Worm. — M. A. Villot, who some time since 
described a peculiar cystic worm (- Staphylocystis ), parasitic upon Glomeris 
limhatus , has discovered another new form in the same myriopod, which he 
notices ( Comptes Rendus, 6 December, 1880) under the name of TJrocystis 
prolifer. It is a very minute creature, measuring only 0*09 millim. (less than 
eh> inch) in length : and one remarkable circumstance about it is that it 
