382 Royal Society : — On the Chemical Intensity 



We have by no means exhausted the list of Mr. Hiley's inaccu- 

 racies. We have, however, said enough to warn teachers from 

 adopting it in middle-class schools. We fear that it may be adopted ; 

 for it is cheap, it will probably be puffed by ignorant writers, and 

 it comes out with an apparent sanction from the Oxford Delegates. 

 But if it is adopted, many an intelligent boy will have all the train- 

 ing he ever gets in an exact science of a far less valuable kind than 

 it might have been had his teacher put into his hands a well- written 

 treatise on "Explanatory Mensuration." 



XLIX. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 228.] 



June 15, 1871. — General Sir Edward Sabine, K.C.B., President, 

 in the Chair. 



HPHE following communication was read : — 



■*■ "On the Measurement of the Chemical Intensity of Total Day- 

 light made at Catania during the Total Eclipse of December 22, 

 1870." By Henry E. Roscoe, F.R.S., and T. E. Thorpe, F.R.S.E. 

 The following communication contains the results of a series of 

 measurements of photochemical action made at Catania in Sicily, 

 on Dec. 22nd, 1870, during the total solar eclipse of that date, with 

 the primary object of determining experimentally the relation exist- 

 ing between this action and the changes of area in the exposed 

 portion of the sun's disk. The attempt to establish this relation 

 has already been made by one of us from the results of observations 

 carried out by Captain John Herschel, R.E., F.R.S., at Jamkandi, 

 in India, during the total eclipse of Aug. 18, 1868. Unfortunately 

 the state of the weather at Jamkandi at the time of the eclipse 

 was very unfavourable, and the results were therefore not of so 

 definite a character as could be desired, and it appeared important 

 to verify them by further observation. The method of measurement 

 adopted is that described by one of us in the Bakerian Lecture for 

 1865 ; the observations were made in the Garden of the Benedictine 

 Monastery of San Nicola, at Catania, the position of which, accord- 

 ing to the determination of Mr. Schott of the United States' Coast 

 Survey, is lat. 37° 30' 12" N., long. l h 0' 18" E. In order to obtain 

 data for determining the variation in chemical intensity caused by 

 the alteration in the sun's altitude during the eclipse, observations 

 were made on the three previous days, during which the sky was 

 perfectly cloudless. 



In the following Table the observations taken at about the same 

 hours are grouped together : — 



