770 Queries and Answers. 



the transit several times between the hours of ten and eleven 

 A.M., and I twice caught a glimpse of it between the hours of 

 one and two p.m. These were the only two periods in which 

 it was visible in this quarter, as I continued patiently watch- 

 ing the whole of the time. — R. J, M, Sept. 4. 1832. 



The Transit of Mercury seen at Colchester. — At half past 

 nine, five minutes before ten, at eleven, and at twenty minutes 

 before twelve o'clock, forenoon, the planet was distinctly seen, 

 like a circular 4)lack spot crossing the sun's disc. — George 

 Scott. Observatory^ Colchester^ May 6. 1832. 



The Transit of Mercury was observed in Ireland^ at the ob- 

 servatory of Trinity College, Dublin, by Professor Hamilton, 

 and also at that of Mr. Sharp, a watchmaker, in Dublin. 

 There was no observation taken at Armagh, owing to the 

 cloudiness of the day. — T. K. Killaloe, Sept. 21. 1832. 



Anchor Frosts (Vol. V. p. 91. 303. 393.). — Sir, 1 perceive that others 

 besides myself have endeavoured to account for anchor frosts. Mr. Carr 

 (p. 395.) says that they never occur except in long and severe frosts ; and 

 that the adhesion of the ice to the stones at the bottom is owing to their 

 acquiring a degree of cold far below the freezing point. He is in error 

 when he says that they never occur except in long-continued frosts, as the 

 walls of ice, which are sometimes raised on the crowns of weirs, are inva- 

 riably (as far as my observations have extended) deposited there before the 

 water in the reservoir above is frozen over : which proves that the frost 

 has not been of long continuance, although it may have been severe. As 

 to what he says about the stones acquiring a degree of cold far below the 

 freezing point, and imparting that coldness to the water, I would just ask 

 how it is that a stone at the bottom of a river acquires this excess of cold, 

 and if it is not more probable that the stones impart warmth to the sur- 

 rounding water. 1 can easily conceive how the stones may, by the action 

 of the sun's rays upon them, warm the surrounding water ; but I do not 

 see how they can impart cold, or, in other words, how their temperature 

 can be reduced below that of the water by which the^ are surrounded. 

 Stones, certainly, impart warmth to the water they are in, in bright wea- 

 ther, as the rays of the sun do not impart much of their warmth in passing 

 through any transparent medium ; but, on coming in contact with any 

 opaque bodies, the heat is absorbed or reflected, as the case may be : and 

 in this way transparent media, such as air and water, acquire a warmth by 

 contact which they would not otherwise possess. Thus, if an anchor frost 

 is followed by a bright day, the rays of the sun impart so much warmth to 

 the stones at the bottom of the river as is sufficient to liberate the ice from 

 them ; and, on such days, thousands of pieces of the ice may be seen float- 

 ing down the streams. Since my former observations (p. 303.) were writ- 

 ten, I have had the satisfaction of finding my view of the subject confirmed 

 by a very eminent chemist ; and if the discussions in your Magazine were 

 to be settled by authority, and not by argument (which, I trust, will never 

 be the case), he is one to whom many would be inclined to appeal, and to 

 whom few would refuse to submit. I am. Sir, yours, &c. — 2\ G. Clitheroey 

 Lancashirey May 2. 1832. 



In J. M.'s communication on this subject, p. 395. line 35., for (the 

 Thames always freezes) " just at the bottom," read " first at the bottom." 

 — J. Z>. 



