424 



The National Physical Laboratory. 



During October a Milne seismograph, Xo. 31, intended to be set up 

 at the University Observatory, Coimbra, was fitted up in the seismo- 

 graph room, at the same height and in the same X. — S. direction as the 

 Kew Instrument, and a series of comparisons were carried out till the 

 end of the year. Several interesting features were noticed, and the 

 results have been embodied in a paper by the Superintendent. 



IV. Experimental AVork. 



Fog and Mist. — The observations of a series of distant objects, 

 referred to in previous ' Reports/ have been continued. A note is taken 

 of the most distant of the selected objects which is visible at each 

 observation hour. 



Atmospheric Electricity . — -The comparisons of the potential, at the 

 point where the jet from the water-dropper breaks up, and at a fixed 

 station on the Observatory lawn, referred to in last year's - Report/ 

 have been continued, and the observations have been taken since 

 March on every day when possible, excluding Sundays and wet days. 

 The ratios of the " curve " and the " fixed station " readings have been 

 computed for each observation, and these have thrown considerable 

 light upon the action of the self-recording electrometer, especially with 

 reference to its insulation. Some direct experiments have also been 

 made on this point. 



The reservoir holding the supply of water for the water-dropper of 

 the self-recording electrometer is supported upon six large " Mascart " 

 insulators, and it was thought that perhaps this system of insulating 

 the tank could be improved upon. 



A quantity of fine paraffin wax, with a high melting point, was 

 procured from Price's Candle Company, Limited, in rectangular blocks, 

 and a number of cylinders of sulphur were cast at the Observatory. 

 Three similar water tanks were supported upon three wax blocks, 

 three sulphur blocks, and three Mascart insulators respectively. Each 

 received a similar definite charge, and the rate of loss of charge was 

 observed. 



The observations — which are to be regarded only as preliminary — 

 extended through May, June, and Jul} T , under various hygrometric 

 conditions. The sulphur and paraffin when new and clean gave much 

 the best values, but after the lapse of a few weeks the rate of loss 

 became very similar for all three species of insulator. The deteriora- 

 tion was apparently due to accumulation of dust, &c. The provision 

 of a hood or cover to the sulphur and paraffin blocks would undoubtedly 

 improve the permanency of their insulating qualities. 



Platinum Thermometry. — The paper by the Superintendent, referred 

 to in last year's Report, has been published in the Royal Society's 

 1 Proceedings,' vol. 67, p. 3. 



