Report of the Kew Committee. 



121 



the Loan Collection of Scientific Apparatus at South Kensington, the 

 costs attendant on its trial at Kew having been defrayed by the Meteo- 

 rological Conncil. 



Photo-nephoscope. — This instrument is still in the hands of Captain 

 Abney, R.E., but experiments have been made with several other 

 forms of nephoscope, and also with a new cloud-camera, designed by 

 the Superintendent. 



Exposure of Thermometers. — Experiments have been continued 

 throughout the year at the Observatory, with the view of determining 

 the relative merits of different patterns of thermometer screens. For 

 this purpose, there have been erected on the lawn a Stevenson's 

 screen, of the ordinary pattern, and a large wooden cage, containing 

 a Wild's screen, of the pattern employed in Russia. Each of these 

 screens contains a dry and a wet bulb thermometer, and a maximum 

 and minimum, all of which are read daily, at 9 A.M. and 9 p.m., their 

 indications being compared with those of the thermograph at the same 

 hours. A third portable metal screen, designed by Mr. De La Rue 

 for use on board Light-ships, which contains a dry bulb thermometer 

 only, is also carried into the open air by the observer, and read at the 

 same time as the fixed instruments. 



The cost of these experiments is borne by the Meteorological Council. 



Glycerine Barometer. — This instrument, devised and erected by 

 Mr. Jordan, as mentioned in last year's Report, has been in successful 

 operation throughout the year, and, in compliance with the request of 

 the inventor, has been continuously observed in conjunction with the 

 mercurial barometer five times daily. In April last, with a view to 

 the more complete removal of the minute quantity of air which bad 

 adhered t© the sides of the tube at the time of filling, and had since 

 risen at intervals into the vacuum, air pressure was applied to the 

 lower surface of the column by means of a force pump, and the 

 glycerine driven up to the top of the tube. The small bubble of air 

 was then expelled through the stoppered aperture, its place being 

 filled by a drop of the glycerine from the cup. 



A complete description of the instrument, by Mr. Jordan, was read 

 before the Royal Society, on January 22nd, and has been printed in 

 their " Proceedings," vol. xxx, p. 105. As a preparatory step towards 

 the discussion of the observations made with the instrument, Mr. 

 Jordan has computed a table for the reduction of its readings to a 

 temperature of 32° E., the mean coefficient of expansion of glycerine 

 having been determined by Professor A. W. Remold to be "000303 

 for 1° F. between 32° and 212°. The value of the glycerine barometer 

 as an instrument of precision cannot be determined until the observa- 

 tions now in process of reduction by Mr. Jordan have been completed. 

 Meanwhile the Committee have decided to continue the periodical 

 readings, and to make several separate series of readings, at frequent 



