320 Obituary Notices of Fellows deceased. 



This appeared as a review of ' A Manual of Photographic Chemistry,' 

 by T. Hardwick, and of a book on * The Tannin Process,' by C. Eussell. 

 It is written in his characteristic style, and gives a good account of the 

 condition of photography at that period, when dry plates were first 

 suggested and discussions were proceeding between artists and 

 photographers. In one of the note-books above mentioned is a list of 

 photographic and chemical apparatus dated December, 1865. 



About 1869 he was experimenting with magnetism, and had a large 

 electro-magnet constructed with the intention of investigating the rota- 

 tion of the plane of polarisation of light in the magnetic field. Later 

 he experimented on the determination of the law of variation of 

 magnetic action with distance, by measuring the throw of a galvano- 

 meter needle due to the current induced in a coil with a soft iron core, 

 when it was placed at different distances from another similar coil 

 through which an electric current was passed. 



In 1872 Lord Salisbury noticed the illumination in the vacuum in 

 the tube of a thermometer placed near an induction coil in action. 

 The following extract relating to similar phenomena, copied, by 

 permission, from a note-book belonging to the latter part of the year 

 1872, from which the first pages are missing, will convey a good idea 

 of his mode of working, whilst it is also of intrinsic scientific interest. 



" Connect one pole of a strong induction coil with the outside of a 

 large thoroughly insulated jar. Take the cap off the jar ; inside of it 

 hang a Geissler tube three inches from the bottom. Let it be hung by 

 a wire connected to earth ; the other pole may be connected to earth 

 or not connected at all. If the positive current is taken to the jar no 

 apparent discharge, silent or other, will pass from jar to tube ; but the 

 tube will lighten. If the negative be taken to jar, a brush will appear 

 at the end of the tube. Break contact. Take out the tube, carefully 

 avoiding to touch the inside of the jar. Then, holding tube, pass it 

 with a quick motion up and down through the mouth of the jar, but 

 never touching ; at each passage up and down the tube will lighten. 

 This may be done for an indefinite number of times, and the light in 

 the tube will strengthen rather than fall off. The tube may be laid 

 aside for half-an-hour, and at the end it will still lighten; bat the 

 effect is slighter. For this experiment tube and jar must be dry, the 

 insulation of the jar must be very good, and the discharge must be 

 strong. 



"This action bears a strong analogy to the action of a closed 

 circuit moved in front of a magnet. The tube is practically a closed 

 circuit, for except in air artificially dried all circuits are so to intense 

 electricity. It is worthy of note that no light is seen unless the tube 

 is taken completely out of the jar at each other stroke. 



