TRANSACTIONS OF SECTION A. 623 



6. On the Photometric Standard of the Kational Physical Laboratory. 

 By Dr. R. T. Glazebrook, F.R.S. 



It was shown by Mr. Paterson in 1904 that the relation between the candle 

 power of the 10-c.p. Vernon Harcourt Pentano Standard at the Laboratory and 

 the humidity of the air is given by the equation, candle-power = 10 + 0"066(10— f), 

 where f is the amount of moisture present measured in litres per cubic metre of 

 air, 80 that the standard condition is when 10 litres of moisture are present and 

 then the lamp has its nominal value 10 c.p. 



In Mr. Paterson's experiments the quantity e was measured in nearly all 

 cases by an ordinary wet-and-dry bulb thermometer, and the observations reduced 

 by the usual formula. 



At the Reichsanstalt an Assmann ventilating hygrometer is employed for 

 the purpose, and the International Commission on Photometry recommended at 

 Ziirich the use of some ventilating hygrometer. 



This has led to a comparison of the two kinds of hygrometers in the still air 

 of the photometer-room, with the result that it has been shown that the ordinary 

 wet-and-dry bulb instrument over the range met with in practice gives results 

 some 20 per cent, higher than the Assmann. The standard humidity then in 

 the previous experiments when measured by the Assmann was 8 litres (not 10) per 

 cubic metre, and Mr. Paterson's formula becomes, candle-power = 10 + 066(8— t). 



The paper discussed the question whether, since a change has to be made, it is 

 desirable to retain the standard humidity at 10 litres measured by the Assmann, 

 and in consequence change the light value at any given humidity of the National 

 Physical Laboratory standard lamps by about 1'3 per cent., or retain the light 

 value and change the standard humidity, and decided in favour of the latter 

 alteration. In this the Gas referees concur. 



The changes which are involved in consequence in the value of the ratio of 

 the Pentane candle to the Hefner and to the Bougie decimal were considered, and 

 it was shown that, adopting as the basis of comparison the results arrived at by the 

 Commission at Zurich, and altering the standard value of the Pentane candle to 

 8 litres humidity, the Pentane candle and the Bougie decimal become practically 

 equal, and each is equal to ten-ninths of the Hefner. 



The practical conveniences of this were first pointed out to the author in a 

 letter from the Bureau of Standards of America, and it is hoped that they will 

 be thought sufficient to lead the International Gas Commission to consider the 

 question of the change at their next session. 



7. Ayi Improved Dry Daniell Pile. By John Brown, F.R.S. 



The author described a few improvements in this pile (which he had originally 

 brought before the Section in South Africa), and gave notes of an experiment 

 indicating its capability of maintaining a potential for several years, suitable for 

 electrifying electrometer needles, &c. A copy of the pile had been made by 

 Mr. John Finnegan, Belfast, two years ago, and found satisfactory and convenient. 



Department op Cosmical Physics. 

 The following Papers were read : — 

 L Is our Climate Changing 1 By Sir John W. Moore, M.A., M.D. 



The author quoted remarkable instances of abnormal weather conditions, 

 particularly in regard to temperature, which had been observed in recent years 

 and in all seasons. Of these perhaps the most notable were the spell of cold 

 weather which made, memorable the Easter week of 1908, and the equally marked 



