238 Rev J. Macgavvie's Thermometrical Ohservations at 



hours, or about a degree and a quarter an hour ; and that it fell 

 from 4 to 7.15 o'clock, G| degrees, or about two degrees an 

 hour. From 10 a. m., when it was 76'', to 4 p. m., when it was 

 at its maximum 82^% it rose about a degree an hour, jthe air re- 

 ceiving heat slowly, and parting with it speedily. 



These registers furnish information only respecting the in- 

 crease and decrease of the heat of the atmosphere, but no ac- 

 curate rule can be drawn from them respecting the minute in- 

 cremental differences, in small portions of time. To secure an 

 accurate account of the regular changes undergone by the air, 

 at very short intervals, I consider a matter of some importance 

 in arriving at any general law that may govern the distribution 

 or increment of heat in the atmosphere. In every climate, the 

 general characters of the days may be easily discovered by ob- 

 servation, and brought under a few heads. Accurate observa- 

 tions of the changes produced on the thermometer during these 

 daysyhowever fewin number, if made at very short intervals, would 

 be much more satisfactory to the meteorologist, than observa- 

 tions made only at morning, noon, and night. These give the 

 extremes of variation, but all the delicate shades and tints of 

 the picture arc lost ; for the changes on some days, in a few 

 hours, are almost innumerable. To use, therefore, a homely 

 Botany Bay simile, we see, by the one mode, only the outside 

 of the bush, but we wish to see all the delicate flowers, leaves, 

 and pods, of which it is composed. The following register of 

 two days, kept in this manner, will show very clearly that an 

 equal and gradual increment very frequently takes place in the 

 early part of the day, but is not to be depended upon when 

 heat has come to its meridional or vertical point, which is most 

 frequently between three and four o'clock r. m. The register 

 was kept with great accuracy to each quarter of a degree, and 

 every variation and change .was marked. The 7th and 8th 

 of January were not fair average days of close suffocating heat, 

 that could be depended upon. The 9th and 10th of January 

 were particularly favourable. It must be recollected, that the 

 sun is now nearly vertical, being on the tropic, and not much 

 more than ten degrees from our zenidi at mid-day ; that he tra- 

 vels from the east to the north, and that the north-west wind 

 blows from the interior opposite to the course of the sun. 



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