Royal Society. 555 



3. " Term- Observations of the Variation of the Magnetic Decli- 

 nation, Horizontal Intensity and Inclination at Milan ; for June 

 1840." By Francesco Carlini, For. Memb. R.S., Director of the 

 Observatory. 



4. " On Ground-gru, or ice formed, under peculiar circumstances, 

 at the bottom of running water." By James Farquharson, LL.D., 

 F.R.S., Minister of the Parish of Alford. 



Tlie author brings forward in this paper several recent observa- 

 tions on the formation of ice at the bottom of rivers, the conditions 

 of which corroborate the views regarding the cause of that phseno- 

 menon, which he presented in a paper on this subject, published in 

 the Philosophical Transactions for 1835 (p. 329)*, namely, that it 

 occurs in consequence of the loss of heat by radiation from the bot- 

 tom of the water, in a manner precisely analogous to the formation 

 of hoar-frost on the surface of dry land, as first explained by Dr. 

 Wells. He then answers some of the objections to that theory pro- 

 pounded in an article, under the title of Ground-Gru, in the Penny 

 Cyclopaedia, and shows that those objections are founded in error, 

 and possess no validity. 



5. " Meteorological Observations made at the Magnetic Observa- 

 tory at St. Helena, from February to October 1840." By Lieut. 

 J. H. Lefroy, R.A. 



6. " Meteorological Observations made at the Magnetic Observa- 

 tory at Toronto, Upper Canada, from January to October 1840." 

 By Lieut. E. J. B. Riddell, R.A. 



7. " Observations on Magnetic Direction and Intensity made at 

 the Observatory at Milan during the 24th, 26th and 27th of January 

 1841." By Prof. Carlini. 



8. " Note on an irregularity in the Height of the Barometer, of 

 which the argument is the Declination of the Moon." By Sir John 

 WilHam Lubbock, Bart., V.P. and Treas. R.S. 



In the Companion to the British Almanac for 1 839, the author in- 

 serted some results which were obtained with a view of ascertaining 

 the influence of the moon on the barometer and on the dew-point. 

 Mr. Luke Howard's researches on this subject {ante, p. 552) having 

 recalled his attention to that paper, he found that some of the results 

 he had given appeared to indicate that the moon's position in decli- 

 nation influences the barometer. In order to render this more ma- 

 nifest, he combines in the present paper all the observations he gave 

 in the Companion to the British Almanac in three categories. These 

 observations correspond to different angular distances of the moon 

 from the sun, or times of transit ; but as the inequaUty of the ocean, 

 of which the argument is the moon's declination, is independent, or 

 very nearly so, of the time of the moon's transit, it is probable that so 

 also is that in the height of the barometer. In this case we may 

 with propriety combine in the same category observations which 

 correspond to similar declinations, although to difl'erent times of 

 transit. The results stated by the author seem to indicate an ele- 



[• An abstract of this paper will be found in Phil. Mag., Third Series, 

 vol. vii. p. 137-] 



