6o 



NA TURE 



[May 17, 1888 



(7b le continued?) 



THE ROYAL SOCIETY CONVERSAZIONE. 



HTHE first conversazione of the season was held on 

 •*■ May 9, and was very numerously attended. More 

 pains than ever seemed to have been bestowed on the 

 arrangements, and the results entirely justified them. As 

 the carefully prepared programme covers eighteen closely 

 printed pages, we can only give a very summary account, 

 of the most important demonstrations and exhibits. 



Following recent precedents, the meeting-room was de- 

 voted to demonstrations by means of the electric lantern, 

 the following being given : image of electric spark, by 

 Dr. Marcet ; Mr. Poulton's teeth of Ornithorhynchus, by 

 Dr. Hickson ; Forth Bridge, by Mr. Baker ; collieries, 

 by Mr. Sopwith. 



The chief exhibits in the other rooms were as follow : — 

 Experiments on the optical demonstration of electrical 

 stress, shown by Prof. A. W. Riicker, F.R.S., and Mr. 

 C. V. Boys. These experiments are similar to those de- 

 vised by Dr. Kerr, the arrangements being modified so as 

 to render them suitable for exhibition in public. Con- 

 ductors of various forms are immersed in bisulphide of 

 carbon and placed between crossed Nicol prisms. When 

 the conductors are oppositely electrified the medium is 

 thrown into a state of stress, and the light which had been ex- 

 tinguished by the analyzing prism is restored. The various 

 forms of conductors employed are — parallel cylinders, 

 concentric cylinders, parallel planes, a plane and cylinder, 

 and plates bent so as to represent a section of a Leyden 

 jar. Many of the phenomena exhibited by crystals 

 in plane polarized light are imitated — e.g. the black 

 cross and the production of colours similar to those in 

 Newton's rings. A bright field can be maintained by the 

 introduction of a plate of selenite between the Nicols, in 

 which case the electrical stress is indicated by change of 

 colour. 



Large electrical influence machine, exhibited by Mr. 

 James Wimshurst. It has twelve disks of 2 feet 6 inches 

 in diameter ; each disk carries sixteen metal sectors. The 

 machine is self-exciting in any condition of atmosphere. 

 It shows large and perfect brush discharge at its terminals. 

 With Leyden jars it will give sparks 13! inches in length. 

 Photographs of flashes of lightning, exhibited by the 

 Royal Meteorological Society. 



Radio-micrometer, exhibited by Mr. C. V. Boys. This 

 is probably the most delicate instrument for measuring 

 radiant heat yet made. It consists of a circuit made of 

 antimony, bismuth, and copper hung by an exceedingly 

 fine fibre of quartz in a strong magnetic field. A scale 

 model of the circuit, twenty times the size or 8000 times 

 the weight, shows the construction of the suspended part 

 of the instrument. The fibre, if magnified to the same 

 extent, would still be finer than spun glass. The propor- 

 tions of the several parts are those which have been 

 found by calculation (confirmed by experiment) to give 

 the greatest possible delicacy. 



Experiments with soap-bubbles, also shown by Mr. 

 Boys. These experiments are arranged to show chiefly 

 the power of an air-film to prevent two bubbles from 

 coming into real contact. Thus, among other experi- 

 ments, the outer of two bubbles may be pulled out until 

 it squeezes the inner one into a long oval, but no real 

 contact takes place. An inner bubble filled with gas will 

 carry up an outer one to which are attached a wire ring 

 and other things without really touching it at all. A 

 bubble will roll down a spiral groove, also made of soap- 

 film, or jump one or two steps at a time down a spiral 

 staircase made of soap-film, without touching the spiral 

 film or being injured in the least. Some of the experi- 

 ments show the effects of diffusion, of vibration, of mag- 

 netism, or of electricity upon bubbles or groups of bubbles. 

 Maps and diagrams illustrative of the recent work of 

 the Geological Survey in the North- West Highlands, 

 exhibited by the Director-General of H.M. Geological 



