140 On the Barometer. 



Rain happen^, among other causes before mentioned, 

 inconsequence oia subtraction of the electric fluid, which, 

 when the air abounds with vapour, is easily conducted ?o 

 the earth ; hence arises the velocity of rain in thunder 

 shoivers. 



In this climate, the hottest time of the day is about 

 three in the afternoon, in consequence of the continued in- 

 Jiuence of the sun, whilst near its greatest height from the. 

 horizon; and the coldest is a short time he/ore sim-rise,\'\z. 

 that time at which our part of the earth has been longest 

 without ihe influence of the sun. 



The hottest month is July; and the coldest month is 

 January; the former, in consequence of the continued 

 strontiest influence of the sun, \\\\\\9,i near its greatest ele- 

 vation from the horizon ; and the latter, in ccnisequence of 

 the continued weakest infiuence of the si;n, uhiist near its 

 least elevut'on from, the hoiizon. The dr'est mojtths are 

 July und August^ and ihe wettest a'e October and I\oieml'er ; 

 the former, in consequence of the small quaniit\ of \\a:er- 

 which has been raised into the atnio^phtrf picvioiisly, and 

 the powerful influence ot the .-un, dur.ng these nionitis, 

 in dissipating the vapours which are raistd ; and ihe latter, 

 in consequence of the inverse elfects of those two causes. 



In like manner, as th.e annual influence of 'ht- sun 

 operates upon the v.eather, producing diftcrenl seasons, re- 

 speclinc wet and drv weather, before staled ; it is not \m- 

 probable, that its diurnal influfiice. being a kind iti epttovie 

 of the former, may, in a smaller degree, have the same 

 efl^ect in producing an ejforf for fair weather, whilst the 

 sun is nearest its greatest diurnal allittide, in consequence 

 of its greater power, at that time, of dissipating vapours, or 

 dispersing clouds. 



The greater or less avidity with which the mercury ap- 

 pears to rise or sink, as exhibited by the greater or less con- 

 vexity or c'.mcavity of the merciuy at the time of observa- 

 tion, the stronger or weaker will be the indication in each 

 instance. 



The surface of the mercury in a barometer is best seen 

 when the tube, at the part lobe observed, is exposed to the 

 light behind, that is, constructed without an opake sub- 

 stance at the back of it. 



The co7ivex or concave surface of the mercurv arises, of 

 course, from the adhesion of the mercury to the tube, in 

 rising or sinking : at each observation of the barometer, 

 therefore, after noticing the variation in height, the index 



should 



