28 



iii:r(»UT — 1MH4. 



On receipt of this information from tlio II0311I Society your Com- 

 mitU'o, takinfjT into consiilcrution, not only tlic late period of the present 

 SeH.sion of J'arlianietit, lnit also the hliort (iiiie that remains before tho 

 dissolution of tlie present Parliament, have determined that it will bo 

 more advantageons to defer appi'oaching Government on the subject till a 

 later period. 



Your (.'oinmittee still wish to hold the matter under further considera- 

 tion, and they therefore ask tliat the Committee be reappointed without a 

 grant of money. 



Noli;. — Since the above Report was drafted the Government have 

 agreed to join tho ' Hiireau International des I'oids ot Mesurea ' 



Report of the Coininitti'e, consisfluf/ of I'rufessor Balfour Stkwakt 

 (Secretarf/), I'rofcssor Stukhs, .Mr. U. JuhnstonkStoney, Professor 

 Sir I f . K. Kosicoi;, Profes.sor Sciiustkh, Captain Ahnky, and Mr. G. J. 

 Symons, aijpointed for the. jtarpoMe of iunwideriiKj the heat 'methods 

 of recordliifj the direct intensiti/ of Solar Radiation. 



This Connnittcc, actin<^ on a suf^'n'cstion made by General Strachey, have 

 chiefly devoted their attention to the subject of a self-recording actiuo- 

 metcr. 



The sell- recording actiuometor of Mr. Winstanley would not bo 

 suitable,' becaase it is influenced by radiation from all quarters. Other 

 actinometers require manipulation on the part of tho observer which would 

 make it almost impossible to make them self-recording. It was suggested 

 by Professor Balfour Stewart that a modification of his actiuometor might 

 bo adapted to self-registration by taking for the quantity to be observed, 

 not the rise of temperature of the enclosed thermometer after exposure for 

 a given time, but the cxce.«s of itsteiuperaturo when continuously expo.sed 

 over the temperature of the envelope. After making some calculations 

 as to the behaviour of such an instrument, Professor Stokes came •'^o the 

 following conclusions : 



(1) The enclosure should be of such a nature as to change its tem- 

 perature very slowly, and of such a material that the various portions of 

 the inteiior should be at the same moment of the same uniform tempera- 

 ture. For this purpose an arrongeraent somewhat similar to that used in. 

 Prof. Stewart's actiiiomoter is suggested ; the outside to consist of polished 

 metallic plates, then a layer of some non-eonducting substance, such as 

 felt, then a thick co})per interior which need not be polished. Into thiS' 

 copper is to be inserted a thermometer which Avill give the temperature 

 of the copper interior from moment to moment. 



(2) In tho middle of the enclosure is to be placed the thermometer, 

 upon which tho heat of tho sun is made to fall by means of a hole in the 

 enclosure, either with or without a lens. This thermometer should be so 



' • This is the case at present, bnt tlieie would not be any great difficulty in 

 modifying it so as to act as loqiiired. It is ijuitu a iniittcr worth consideration 

 whctlier a dilTorential air-thermometer would not be very suitable, one bulb silvered 

 and tho other blackened or of green fila-ss, as I suggested to the Meteorological Council 

 some years back, liy this means only one reading would be necessary, whilst in the 

 plan suggested two would have to be recorded, and the measurements would be^ 

 more difiicult.' (^Xoti- hij Cupiain Ahncij.') 



