Scientific Intelligence. — Meteorology. 377 



to attract it ; and I think that I have been told, that, when 

 this phenomenon takes place at night, a glimmering of light is 

 observed over every part of the rigging. But when the squall 

 has removed to about half-a-mile beyond the ship, exactly the 

 same appearances return by which the squall was characterised 

 in coming off the shore, and before reaching the same distance 

 from the ship. The lightning is again seen to be descending in 

 continued sheets, and in such abundance as even to resemble 

 the torrents of rain themselves which accompany the squall. 

 These squalls take place every day during a certain season of 

 the year, called the Harmatan season. The jet black clouds be- 

 gin to appear moving from the mountains about nine in the 

 morning, and reach the sea about two in the afternoon. Ano- 

 ther very singular fact attending these tornadoes is, that 

 after they have moved out eight or nine leagues to sea, when 

 they become apparently expended, the lightning is seen to rise 

 up from the sea. The violence of the wind, during the conti- 

 nuance of the squall, is excessive. — D. M. Milnegraden. 



2. Human Voice heard at a great distance. — The distance at 

 which the human voice is heard, has been long well known. A re- 

 markable instance of this fact is mentioned by Captain Parry, 

 in a former Number of this Journal, in which the human voice 

 was heard at a distance of 1.2 English miles. Dr Young in 

 his Lectures on Natural Philosophy, states, on the authority of 

 Derham, that a man at Gibraltar heard the human voice at the 

 distance of ten English miles. — Young's Lectures, vol. ii. 



p. 9.m. 



3. Method of reducing Barometrical Observations to a 

 standard Temperature. — Various tables have been published by 

 different authors for reducing barometrical observations to a 

 standard temperature. Though great care seems to have been 

 bestowed in drawing up some of these tables, it is singular how 

 little discrimination has been employed in selecting the data, 

 from which they have been calculated. Many retain the rate 

 of expansion according to De Luc, neglecting the determinations 

 of later experimenters, and some of them have even made the 

 relative expansion of mercury in glass tubes, the basis of their 

 calculations, not reflecting that the diminution of specific gavity 



