Intelligence and Miscellaneous Articles. 233 



collar, and a second screw acting horizontally, and at right angles 

 to the line of direction of the needle. By a little adjustment, the 

 two points on the needle are made to coincide in the field of view 

 of the telescope of the sextant ; and the radius is then moved until 

 the meridian mark (at such a distance as to make the parallax of 

 the instrument inappreciable,) coincides with them. The degrees 

 read off give twice the horizontal divergence of the needle. If an 

 east point can be easily procured, a means of correcting this result 

 will readily suggest itself. This mode may prove of great import- 

 ance in experiments on diurnal variation, and as it requires but 

 trifling expense, the investigation is opened to many who were 

 deterred by the price of the apparatus ordinarily in use. With the 

 dipping needle the process is precisely similar, the axis being so 

 constructed that the points can be observed in conjunction, and a 

 horizontal mark at a distance previously obtained. 



(From a Correspondent.) 



ON THE CAUSE OF THE METEOROLOGICAL PHENOMENA 

 OBSERVED IN THE MOUNT'S BAY BY MR. HENWOOD. 



To the Editors of the Phil. Mag. and Journal of Science. 

 Gentlemen, 



The occurrence to which Mr. Henwood has alluded in your last 

 Number (p. 105.), namely, the formation of clouds on Paul Hill, while 

 the rest of the atmosphere was almost free from clouds, is easily ac- 

 counted for, on the principle that vapour exists in the atmosphere 

 in a quantity proportional to its temperature. If the temperature 

 of the atmosphere be high, in comparison with what it had been, the 

 heavens will be clear ; if it become lower, vapour will be visible ; or 

 if still lower, rain will descend. The temperature of the sea in win- 

 ter (as is well known) is usually higher than that of the land, espe- 

 cially in the beginning of winter, and in the evening*; clouds, 

 therefore, at these times are frequently seen forming on the hills as 

 the breeze passes from the sea. The sea gives out heat, which pre- 

 serves what would otherwise be clouds in the form of transparent 

 vapour : the land withdraws heat from the vapour, and causes the 

 formation of clouds. 



Of course, the relative temperature of places varies; consequently, 

 clouds are sometimes seen over the sea, while the land is clear. 



I remain, Gentlemen, respectfully, 

 February 4, 1834. j. F. 



[Our Correspondent's explanation is substantially correct : no 

 difficulty, nor any difference of opinion, however, could exist upon 

 the subject. — Edit.] 



ON LACTIC ACID. BY MM. J. CJAY-LUSSAC AND J. PELOUZE. 

 Various opinions have at different times been entertained as to 

 the nature of lactic acid. It was discovered by Schcele in 1780, 



* Mr. Henwood't observations wure made in November, in the evening. 

 Third Series. Vol. 4-. No. 21. March 1834. 2 II 



