March 7, 1889] 



NATURE 



445 



larger scale with oil of turpentine, and he detected the 

 existence of currents, which are in accord with the view 

 that the unelectrified liquid flows up the exterior of the 

 cylinder, becomes electrified by contact, apd is repelled 

 down its axis. In view of this explanation, and the move- 

 ments assumed can be clearly seen in the phenyl thio- 

 carbamide, the performance of the experiment on a small 

 scale is not without interest. The possibility of the forma- 

 tion of such violent up-and-down currents in so small a 

 space must depend upon a very nice adjustment between 

 the properties of the liquid and the forces in play. It is 

 obvious that such movements of the liquid must be a 

 disturbing element in any attempt to make the lines of 

 electric force visible. 



Again, if a solid powder be suspended in a liquid into 

 which electrified solids are introduced, it tends to 

 accumulate round one of the poles. This subject has 

 been investigated by W. Holtz. Sometimes the powder 

 appears to move in a direction opposed to that in which 

 the liquid is streaming. Sometimes two powders will travel 

 towards different poles. 



If powdered antimony sulphide be placed in ether, it 

 settles at the bottom of the liquid, and if either two wires 

 insulated with glass up to their points, or two vertical 

 plates be used as electrodes, on exciting them slightly the 

 solid particles arrange themselves along the lines of force. 

 If the electrification be increased, they cluster round the 

 positive pole. On suddenly reversing the electrification 

 by means of a commutator, they stream along lines of 

 force to the pole from which they were previously repelled. 

 Other methods of obtaining the lines of force have been 

 devised. They can, for instance, be shown by crystals 

 of sulphate of quinine immersed in turpentine. 



The tendency of the lines of force to separate one from 

 the other was illustrated by Quincke's experiment. A 

 bubble of air is formed in bisulphide of carbon between 

 two horizontal plates. It is in connection with a small 

 manometer, and when the plates are oppositely excited, 

 the electrical pressure acting at right angles to the lines 

 of force, being greater in the liquid than in air, compels 

 the bubble to contract. 



Kerr's experiments depend upon the fact that, since the 

 electrical stress is a tension along the lines of force, and 

 a pressure at right angles to them, a substance in which 

 such a stress is produced assumes a sertiicrystalline con- 

 dition in the sense that its properties along, and perpen- 

 dicular to, the lines of force are different. Light is there- 

 fore transmitted with different velocities according as the 

 direction of vibrations coincides with, or is perpendicular 

 to, these lines ; and the familar phenomena of the pas- 

 sage of polarized light through crystals may be imitated 

 by an electrically stressed liquid. 



The bisulphide of carbon used must be dry, and, to 

 make the phenomena clearly visible, it is necessary that 

 the light should travel through a considerable thickness. 

 Thus, to represent the stress between two spheres, elong- 

 ated parallel cylinders should be used, the axes of which 

 are parallel to the course of the rays of light. These 

 appear on the screen as two dark circles. Between 

 crossed Nicols, the planes of polarization of which are 

 inclined at 45" to the horizontal, the field is dark until 

 the cylinders are electrified, when light is restored in the 

 space between them. 



If parallel plates with carefully rounded edges, and 

 about 2 millimetres apart, are used, the colours of 

 Newton's rings appear in turn, the red of the third 

 order being sometimes reached. If one plate is convex 

 towards the other, the colours of the higher orders appear 

 in the middle, and travel outwards as the stress is in- 

 creased. The experiments may be varied by using two 

 concentric cylinders, or two sheets of metal bent twice at 

 right angles to represent a section through a Leyden jar. 

 In the first case a black cross is formed ; and in the 

 second, black brushes unite the lower angles of the images 



of the edges of the plates. By the interposition of a 

 piece of selenite, which shows the blue of the second 

 order, two of the quadrants contained between the arms 

 of the cross become green, and the others red. In like 

 manner the horizontal and vertical spaces between the 

 inner and outer coatings of the "jar" become differently 

 coloured. 



There are several phenomena connected with the stress 

 in insulators which present considerable difficulties. Thus 

 in a solid it is found impossible to restore the light 

 between crossed Nicols by a uniform electrical field. That 

 the non-uniformity of the field has nothing to do with the 

 phenomenon in liquids, though at first disputed, is now 

 generally admitted. It may be readily proved by means 

 of a Franklin's pane, of which half is pierced into 

 windows. The glow is much weakened by thus removing 

 part of the uniform field, though it is thus made much 

 less uniform. 



Again, though most dielectrics when placed in an 

 electric field expand, the fatty oils contract. Prof. J. J. 

 Thomson has recently pointed out that this indicates that 

 another set of strains are superposed upon those assumed 

 in the ordinary explanations of these phenomena, and by 

 which they may be neutralized or overcome. 



In experiments with carbon bisulphide it is necessary 

 to take every precaution against fire. For this purpose 

 the cell which contains the liquid should be immersed in 

 a larger cell, so that if — as sometimes happens — the 

 passage of a spark cracks the glass the liquid may flow 

 into a confined space. This should stand in a tray with 

 tumed-up edges, and an extinguisher of tin plate should 

 be at hand to place over the whole apparatus. No Leyden 

 jars should be included in the electrical circuit. The 

 difficulties which formerly arose in the exhibition of ex- 

 periments in statical electricity owing to the presence of 

 moisture in the air of a lecture-room are now immensely 

 reduced by the Wimshurst machine, which works with 

 unfailing certainty under adverse conditions. A new and 

 very beautiful machine was kindly lent by Mr. Wimshurst 

 for the purposes of the lecture. 



NEW BUILDINGS AT CAMBRIDGE FOR 

 PHYSIOLOGY AND ANATOMY. 



T^HE energy and success of the Cambridge teachers of 

 ■■■ science are once more demonstrated by the proposal 

 to build new laboratories, with a large lecture-room, for 

 anatomy and physiology, and a museum and dissecting- 

 room for human anatomy, on a scale commensurate with 

 the importance of the medical and biological school. The 

 present physiological laboratories, which ten years ago 

 were a great advance upon the mere make-shift arrange- 

 ments that had previously done duty, are now disagreeably 

 overcrowded. At present. Prof. Foster's elementary class 

 is attended by between 190 and 200 students; and the 

 several advanced classes have from twenty to thirty-five 

 students. In the laboratory there are now only places for 

 ninety students of histology ; but accommodation has 

 been provided for about seventy more in a temporary 

 building attached to the museum. Inasmuch as the 

 students of the elementary class must all go through 

 the histological course, lasting throughout three terms, 

 it is evident that they can be accommodated only by 

 relays, and that in order to accommodate the advanced 

 students, who have no proper places of their own, much 

 crowding must take place, whereas the advanced students' 

 work-places ought not to be disturbed, as these students 

 need opportunities for continuous work. For chemical 

 physiology there are only eight places available, and there 

 is one fairly large room for physical physiology ; there 

 is no adequate lecture-room. 



The proposed buildings have once been deferred, plans 

 having been prepared in 1884; but it is hoped that the 



