jO 



meter, 

 in the 

 be so 



ulty in 

 leration 



ilvored 

 Council 

 in the 



uld be 



(IN DIKKCT IXTKNSri'Y OV Sol, All UADIATION. 



S9 



constrnctod as to ho n-adily RnsceptihU; of solar influcncos. Tt is prcposofl 

 to muko it of prccn glass (a good ahsorher and radiator), and to givo it 

 a flattered snrfaco in the direction pcrpendicnlar to the hght from the hole. 



Sueli an iiiHti'iiniont sliould he no adjusted as to receive the snn's light 

 continuously ihrougli the hole, and tlio ohjects of I'ccord would he the 

 siiuultancouH heights of the two thermometers, the ono giving the tem- 

 perature of tlio enclosure, and the otliorof the central thermometer. There 

 are I'.vo conc(!ival)lo methods by wliich the necessary adjustment with 

 regard to the sun's light might be secured, namely, («) the enclosuro 

 might be subject to an ecpiatorial motion so as to follow the sun, or (/5) 

 the enclosure might be kept at rest^ and the solar rays kept upon the holo 

 by a liehostat. Captain Abm^y is of opinion that the latter arrangement 

 is, mechanically, much preferable to the former. 



As the direction of the earth's axis may be chosen as that into which 

 the sun's light is to bo reflected, a heliostat of a very simple construction 

 will sufhce; and as the angle of incidence on the mirror of such a heliostat 

 chanye-i only very slowly with the season, tliero is no difliculty in applying 

 the small correction required for the change in the intensity of the reflected 

 heat consequent on the change in the angle of incidence. It is assumed 

 that the mirror of the heliostat is a speculum. 



It has been remarked by General Strachey that some such instrument 

 as this now suggested, even if not made self-recording, would have the 

 advantage of giving an observation without the objectionable necessity of 

 putting the light on for a given time and then shutting it ofl", operations 

 oidy suitable for trained observers. We think that it would be desirable 

 to construct an enclosure with its two thermometers such as herein 

 recorded. In all probability tiie loan of a heliostat and of an actinometer 

 might be obtained. By aid of the heliostat the sun's light might be kept 

 continuously upon the holo of the enclosure. The two thermometers 

 would be read, and the results compared with the simultaneous reading 

 of an ordinary actinometer. I3y .such means it is believed that the best 

 method of constructing such an instrument and observing with it might 

 be found. 



We would therefore ask for a continnanco of our Committee, with the 

 sum of ;}0/. to bo placed at our disposal for the purpose herein specified. 



Report of the Committee, consistlnr/ of Professor Or. Carey P'ostek, 

 Sir William Thomson, Professor Ayrton, Professor J. Perry, 

 Professor W. G. Adams, Lord Paylekhi, Professor Jenkix, Dr. O. 

 J. Lodge, Dr. John Hopkinson, Dr. A. Muirhead, Mr. W. II. 

 Preece, ^Ir. Heuih:rt Taylor, Professor F'ERETT, Professor 

 Schuster, Dr. J. A. P'LE.NHNtf, Professor G. F. Fitzgerald, Mr. P. 

 T. Glazehrook {Secretary), Professor Chrystal, Mr. H. Tomlin- 

 sox, and Professor W. Garxett, appointed for the purpose of 

 constructing and issuing practical Standards for use in Elec- 

 trical Measurements. 



The Committee report that during the year the construction and testing 

 •of standards of electrical resistance has been proceeded with. The 

 toils of 10, 100, 1,000, and 10,000 B.A. units, mentioned in the last 

 Report, have been compared with the standard unit coils. An account 



