58 EEPOET — 1880. 



Two platinum wires, in connection witli r and / respectively, are fixed 

 into opposite ends of the tube. 



The tube is then exhausted till a Crookes' vacuum is obtained, when 

 the arm K becomes a radiometer arm. 



A small slip of magnetised watch-spring is attached to B, so that a 

 fixed magnet can be so placed as just to bring the carbon point and anvil 

 in direct contact. 



A strong light being then turned on B, the screen acts like a radiometer 

 arm, moves back, separates the carbon points, and contact is broken. 



By attaching a simple screen to the pendulum, it therefore becomes 

 possible to cause the pendulum, by alternating, to admit and cut ofi" light 

 from B, and so produce alternate make and break, entirely as required 

 by the escapement, without employing any actual contact on the pen- 

 dulum. 



The chief difficulty we now find is a tendency of the carbon points to 

 stick, and some experiments are now being made relative to this matter. 



Four relays on the principle described have been constructed and are 

 in the hands of the committee for experiment, and Mr. Gill has, besides, 

 a model of the escapement, and a pendulum with which experiments are 

 being carried out. 



A sum of 12Z. 12s. has been expended out of the grant of SOI., and 

 the Committee requests that the balance of the grant should be allowed to 

 be applied to the same research. 



Second Beport. 



Since the foregoing report was sent from the Cape by Mr. Gill, I have 

 devoted much time in developing the mode of electric contact-making by 

 radiation. 



In the above report for last year is described a form of the radio- 

 relay which at the time seemed to give the most promising results 

 of any that I had tried. Four of these were made, as mentioned by Mr. 

 Gill, one of "which he took out to the Cape, experimented with, and in the 

 report he mentions the chief difficulty as being that of the tendency of 

 the contacts to stick together when work is being done by the current. 



In the case of using contacts of metal, such as platinum, this diffi- 

 culty is insurmountable, for the reason that the power required to sepa- 

 rate the contacts when once closed is far greater than that which can be 

 obtained from any source of radiation that could be used for our purpose. 

 This point I had settled some time back, and had almost abandoned the 

 idea of success, when the discovery of the microphone by Prof. Hughes 

 suggested to me the idea of using carbon contacts. I then commenced 

 working on the subject again, and experimented with a great number of 

 instruments of different forms. 



The form of a pendulum with the contacts near the point of suspension 

 has at present given the most satisfactory results. Fig. 5 represents the 

 pendulum form of the radio-relay ; a is a strip of moderately thin alumi- 

 nium, to the lower end of which is attached a plate of silver flake mica 

 b, blackened on the outer face ; c is a clear mica screen, the same size as 

 the plate b, also attached to the lower end of a, enclosing a space of 

 about 6 mm. between the two plates. 



The strip of aluminium a is suspended by two springs of soft iron 

 wire, beaten out flat and very thin in the centre, represented by d in 



