212 



M eteorological Obser vat ions. 



[Jan. 



The barometer employed in the observations of the 29th, and up to 

 1 p. m. of the 30th, was the standard barometer which has hitherto 

 been in use. At 2 p. m. the northern do/'rs of the Observatory were 

 burst in, and the moveable roof blown open, whereby the standard 

 barometer and thermometer, at one rude rush of the wind, were, with 

 telescopes, tables and chairs, overturned and broken. I was conse- 

 quently under the necessity of registering the first barometer which 

 came to hand (one by Harris), whose indications are given above 

 for 2 p. m. et seq. To discover the error of this barometer, and to 

 replace as well as I could the standard which had been broken, I 

 availed myself of the old frames of the two standard barometers just 

 alluded to (which had not been damaged), and filled two tubes which 

 are now in use. In the first place it was desirable to examine the scales ; 

 this I was enabled to do very satisfactorily, by means of a standard two 

 feet scale by Adams with the assistance of a pair of beam compasses. 

 The divisions on one of the frames (Dollond's) agreed perfectly with the 

 standard scale ; but the other frame (Gilbert's) was in error ,025. In 

 the next place the purity of the quicksilver was to be ascertained— 

 having failed for several days to meet with any means of distilling 

 quicksilver or any one who could assist me in this respect, I had 

 recourse to washing it repeatedly in diluted nitric acid, which combin- 

 ing with the bismuth or antimony with which quicksilver is generally 

 adulterated, leaves the quicksilver quite pure. I have not yet deter- 

 mined its specific gravity to any great degree of accuracy, for want of 

 proper means ; but from two separate experiments agreeing very well 

 with one another, it came out 13,645 ; shewing that a correction 0,033 

 subtractive should be applied to the readings, to obtain those which 

 should obtain were the quicksilver of standard purity. Doubtful if 

 this or any correction was necessary, from the apparent purity of the 

 quicksilver ; I procured some very bad bazar quicksilver, and washed it 

 with nitric acid in the same way as practised before on quicksilver, 

 procured from the Medical stores ; when the same tube, successively 

 filled with the two sorts of quicksilver, did not differ ,010, of an 

 inch in its indications. The quicksilver was not boiled in the tube, 

 by reason of the danger attendant upon such an experiment ; but both 

 the tube and quicksilver were heated before being used, to a tempera- 

 ture of about 180 degrees. To be sure that no air or moisture existed 

 in the tube or quicksilver, I have refilled one of the tubes three succes- 

 sive times, and found a difference in the third decimal place only. The 

 particulars of these barometers are as follows : 



Correction of the divisions 



Diameter of bore of the tube 



Correction due to capilliary action. 

 Relative indications 



DollonoVs scale. 

 Inches 0,000 

 „ 0,19 

 „ +0,061 

 „ 29,958 



Gilbert's scale. 



Inches —0,025 

 „ 0,28 

 „ 4-0,031 

 „ 30,020 



