94 



NATURE 



[May 28, 1891 



point was reached, and afterwards diminished again, thus show- 

 ing that the high resistance of a nearly perfect vacuun;i is in no 

 way due to the presence of the electrodes. One peculiarity of 

 the discharges was their local nature, the rings of light being 

 much more sharply defined than was to be expected. They were 

 also found to be most easily produced when the chain of mole- 

 cules in the discharge were all of the same kind. For example, 

 a discharge could be easily sent through a tube many feet long, 

 but the introduction of a small pellet of mercury in the tube 

 stopped the discharge, although the conductivity of the mercury 

 was much greater than that of the vacuum. In some cases he 

 had noticed that a very fine wire placed within a tube on the 

 side remote from the primary circuit would present a luminous 

 discharge in that tube.— Some experiments on the velocities of 

 the ions, by Mr. W. C. D. Whetham. In studying electrolysis 

 the question as to whether there is any transference of solvent 

 when a porous wall is absent presented itself to the author. The 

 ordinary methods of testing for transference, such as by increase 

 of pressure, or by overflow, not being available, when there is no 

 diaphragm, the author used difTerent coloured solutions of the 

 same salt, such as cobalt chloride in water and in alcohol, the 

 former of which is red and the latter blue. By putting the 

 solutions into a kind of U-shaped tube any change in the position 

 of the line of junction of the two liquids could be measured. 

 Two aqueous solutions in which the anion was the same were 

 also tried, one combination being cupric chloride and common 

 salt, and in this case the line of demarcation traversed about 

 7 inches in three hours. The results hitherto obtained by this 

 method agreed fairly with those found by Kohlrausch. — On 

 the resistance of some mercury standards, by Mr, R. T. Glaze- 

 trook.F.R.S. In 1885, M.Benoit, of Paris, supplied the author 

 with three mercury standards, nominally representing the Paris 

 Congress ohm, now commonly known as the legal ohm. Tests 

 of these standards were described in a paper read before the 

 Physical Society in 1885 by the present author. Recently he 

 had occasion to compare two of the standards with the British 

 Association coils. The mean of many concordant results gave 

 the resistance of one of the mercury standards (No. 37) as 

 1-01106 B.A.U., whilst that of the other (No. 39) was i 01032 

 B. A. U. Expressing them in legal ohms the present resistances 

 are (No. 37) 0-99986 and (No. 39) 0-99913, whilst in 1885 the 

 values obtained were (No. 37) 0-99990 and (No. 39) 0-99917. 

 This shows that within the limits of experimental error the ratios 

 of the mercury standards to the B. A. coils have remained practi- 

 <;ally unchanged during six years. The numbers given above 

 are based on Lord Rayleigh's determination of the specific 

 resistance of mercury, which differs appreciably from that found 

 by Mascart and other observers. Taking the mean of the later 

 concordant determinations, the values of the mercury standards 

 expressed in legal ohms become (No. 37) I '00033 and (No. 39) 

 0-99959. The values given by the maker were 1-00045 and 

 o '99954 respectively, showing a very close agreement. The 

 author also found that refilling No. 37 from the same sample of 

 mercury produced no appreciable change in its resistance, whilst 

 No. 39 was somewhat affected by a similar operation. Experi- 

 ments on the co-efficient of increase of resistance of mercury with 

 temperature gave the value 0-000872 as the mean coefficient 

 between 0° and 10° C, a number rather less than that obtained 

 by Kohlrausch. — On an apparatus for measuring the compressi- 

 bility of liquids, by Mr. S. Skinner. The apparatus consisted 

 of a large spherical flask, with a long narrow neck containing the 

 liquid to be experimented upon, the lower part of which was in 

 communication through a stopcock and flexible tube with an 

 adjustable reservoir. By raising or lowering the latter the flask 

 could be easily filled or emptied or the quantity of liquid ad- 

 justed. The flask was inclosed in a bell jar, whose interior 

 was in communication with a pump and barometer gauge. So 

 sensitive was the arrangement that the compression of water 

 produced by blowing into the jar caused the liquid to descend 

 about I centimetre in the neck of the flask. This movement 

 corresponded with a change of volume of about half a millionth. 

 The coefficient of compressibility had been tested at different 

 temperatures, and the results were not very different from those 

 obtained by Tait and others. The influence of salts in solution 

 in changing the compressibility had also been tested, and a 

 great difference in this respect found between electrolytes and 

 non-electrolytes. — Some measurements with the pneumatic 

 bridge, by Mr. W, N. Shaw. The action of the apparatus is 

 analogous in many respects to the Wheatstone's bridge, and its 

 ■object is to compare the pneumatic resistances or conductivities 



NO. 1 1 26, VOL. 44] 



of various orifices, channels, tubes, &c. The proportional arms 

 are represented by two circular holes in thin plates of mica, the 

 third arm by an aperture provided with a sliding shutter adjust- 

 able by a screw, and the fourth might consist of any aperture or 

 tube whose conductivity was to be determined. The several 

 apertures are pneumatically connected by large wooden boxes. 

 The battery takes the form of a Bunsen burner with a long 

 chimney, whilst the galvanometer is represented by a glass tube 

 connecting opposite chambers, and containing a vane which sets 

 itself at right angles to the tube when no air current is passing. 

 The apparatus is remarkably sensitive to movements of the 

 shutter, and on starting or stopping the draught after balance 

 had been obtained, effects analogous to those produced by self- 

 induction are observed. By its use it has been found that 

 bevelling off one side of a hole in a thin plate increases the 

 pneumatic conductivity of the aperture very considerably, parti- 

 cularly when the bevel is on the egress side. Another inter- 

 esting result is that for square-ended tubes of given size the 

 conductivity first increases as the length is made greater, and 

 afterwards diminishes with further increase of length. Putting 

 a flange on the outlet end reduces the anomalous effect, whilst a 

 bevelled mouthpiece similarly placed causes it to disappear. In 

 the discussion on Prof. Thomson's paper. Prof. Fitzgerald said 

 the beautiful experiments were likely to lead to very important 

 results. He did not quite understand how placing a fine wire 

 in a vacuum tube could prevent the luminous discharge, for if 

 the wire was on the side remote from the primary, and if there 

 was any great increase in specific inductive capacity, he would 

 have expected the air to screen the wire. Prof. Lodge asked 

 for further information as to the action of the magnet in 

 preventing the afterglow, and in some cases precipitating a 

 luminous discharge. The experiment with the exhausted bulb 

 within the bell jar was also difficult to understand, and he did 

 not see why one of Prof. Thomson's two suppositions must 

 necessarily be true. The President inquired whether Prof. 

 Thomson had tried Mr. Crookes's experiment, in which the 

 electric pressure necessary to produce a discharge was greatly 

 lessened by putting a phosphorescent material in the tube. 

 Prof. Thomson, in reply, said he had not tried the experiment, 

 but the phosphorescence he had observed was of quite a different 

 character from that produced in Mr. Crookes's tubes. To Prof. 

 Fitzgerald he said the action of the wire was probably a question 

 of time, and thought the whole field was in some way thrown on 

 the wire and thus discharged. In reply to Prof. Lodge, he had 

 not ascertained the true nature of the effect of a magnet on the 

 glow, but he believed the glow to be due to a combination 

 which might be prevented or facilitated by the action of the 

 magnet causing the density to be different in different parts of 

 the bulb, M. Guillaume, in discussing Mr. Skinner's paper, 

 described the methods used by Sabine, Jamin, and others, in 

 determining the compressibility of liquids, and pointed out their 

 defects. The chief difficulty in such experiments was in finding 

 the compressibility of the reservoir. Numbers expressing the 

 compressibility of mercury obtained by different observers were 

 given, the best values varying between 0-0000039 and 0-0000040. 

 — On the motion of Prof. Ayrton, seconded by Prof. Riicker, a 

 hearty vote of thanks was accorded to the authors for their 

 valuable and interesting communications, and for the kind 

 manner in which the Society had been received and entertained 

 by the Cambridge members. Prof, Thomson and Mr, Glaze- 

 brook acknowledged the vote. 



Geological Society, May 6.— Dr, A. Geikie, F,R.S,, 

 President, in the chair, — The following communications were 

 read:— On a Rhaetic section at Pylle Hill or Totter Down 

 Bristol, by E. Wilson. In a deep railway-cutting at Pylle Hill, 

 the Rhsetic beds, having a thickness of not more than seventeen 

 feet, are exposed between the Tea-Green Marls and the Lower 

 Lias. There is no doubt as to the division between the Rhaetic 

 and Keuper beds in this section, but the line of demarcation 

 between the Rhsetic and the Lias has always been a matter of 

 uncertainty in the West of England. In connection with this 

 subject the term " White Lias," as applied to beds some of 

 which are Rhsetic and others Liassic, is held to be unsatisfactory. 

 The author takes a limestone which is the equivalent of the 

 Gotham Marble as the highest Rhsetic bed in the section 

 described. He divides the Rhaetic beds of the cutting into an 

 Upper Rhsetic series and Avicula contorta Shales. The in- 

 timate connection betwixt the Tea-Green Marls and the Red 

 Marls of the Upper Keuper is well displayed, whilst there is a 



