70 Royal Society : — 



silica in the usual manner, a slight excess of ammonia was added 

 to the hydrochloric-acid solution of the earths, and then some oxalic 

 and hydrochloric acids, which left undissolved apparently pure zir- 

 conia that had passed into an imperfectly soluble state. To the 

 solution so much ammonia was added as to give a very copious pre- 

 cipitate, but yet to leave the solution with a very decided acid reac- 

 tion. After removing the precipitate, which was chiefly oxalate of 

 zirconia almost or quite free from jargonia, excess of ammonia was 

 added to the solution, and the washed precipitate digested in dilute 

 hydrochloric acid, to remove peroxide of iron. The insoluble por- 

 tion must have been approximately pure oxalate of jargonia ; for it 

 gave the characteristic spectra described in remarkable perfection. 

 Though this method succeeded far better than I anticipated, I do 

 not yet understand the exact conditions requisite to ensure success, 

 and have been prevented by absence from home from making further 

 experiments. 



" Solar Radiation." By J. Park Harrison, M.A. 



In a communication which the author had the honour of making 

 to the Royal Society in 1867 *> it was shown, from observations of 

 the black- bulb thermometer and Herschel's actinometer, that maxi- 

 mum effects of solar radiation occur at Greenwich, on the average, 

 some weeks after the summer solstice, and about two hours after 

 midday, when the atmosphere would appear to be charged with a 

 considerable amount of vapour. 



These results accord with the fact that the highest readings of the 

 solar thermometer are met with in India in districts of great relative 

 humidity f, the explanation of the phenomenon being, as the author 

 ventured to suggest in the paper above alluded to, that an increase 

 of insolation is produced by radiation from cloud and visible vapour. 



During the two years which have elapsed since the spring of 1867, 

 whenever the state of the sky and other circumstances permitted, 

 special observations have been made for the purpose of ascertaining 

 with greater certainty the nature of the relation between insolation 

 and humidity. 



Before proceeding to state results, it will afford additional proof 

 that a connexion between the phenomena really exists, if a passage 

 in the appendix to a work by the late Principal of St. Andrews, 

 until very recently overlooked, is quoted in support of the fact. Mr. 

 Forbes, writing some years ago, employs much the same words that 

 were used in the paper above referred to : — " Cloudy weather, if the 

 sun be not itself greatly obscured, apparently increases the effect of 

 solar radiation " %. 



The action, however, does not appear to be confined to days on 

 which there is visible cloud ; for even on cloudless days (so called) 

 very high readings of solar radiation seem to be due to the presence 



* Proc. Koy. Soc, Feb. 1867. 



t Proc. Eoy. Soc, March 1865. 



| Travels through the Alps of ^avoy, App. III. p. 417. 



