GREAT MALVERN AND LONDON. 23 



the shade rapidly increases in the day time — passing above the mean 

 of the season ; whereas, in winter, during clear weather, the heat 

 of the sun hardly counteracts the influence of terrestrial radiation : 

 hence, in the clear sunny days of winter, the temperature of the air 

 advances but little — the mean of this period being governed by va- 

 pour ; so that it is not at all uncommon for the thermometer to rise 

 between sunset and sun-rise from 10° to 15°. This has been no- 

 ticed in a minor degree, as early as the month of October. 



The period of the maximum of the thermometer will depend 

 upon several circumstances : during summer, if the morning is 

 bright and fair, followed by clouds and wind in the afternoon, it 

 will occur before noon — so it will if the sun shines in the morning 

 and it rains in the afternoon : but if the morning is wet and the af- 

 ternoon fine, the maximum is observed later. In winter, the maxi- 

 mum of the twenty-four hours will occur in the middle of the day 

 or the middle of the night, or at any other period, being governed 

 by the movements of the great body of aerial vapour and its con- 

 densations. Clouds and rain do not always accompany the high 

 temperature due to warm vapour, though they are not long in fol- 

 lowing it : thus, in the Journal from which these remarks are taken, 

 is the following: — "December 29, 1833, 11 p.m. Here is, to- 

 night, a high temperature, (51°) and a high dew-point, (50°), yet it 

 is veryjlne, the wind is high, and some heavy clouds are present,— 

 but the intervals of blue shy are large, and the moon and stars bril- 

 liant;" but the next remark, the following morning at 9 a.m., is,- — 

 " heavy clouds and rain, and rain during the night." 



Meteorological registers, in general, are not much to be relied 

 on: the observations are recorded without any attention either 

 to the accuracy of the instruments employed, or to the circum-' 

 stances in which they are placed. In the Philosophical Magazine, 

 the only periodical exclusively devoted to science now published in 

 London, are the details of a register kept at the gardens of the 

 Horticultural Society ; and we should have expected that here some 

 confidence might have been placed, had we not remarked the very 

 great difference between these details and those of the Journal of 

 the Royal Society, at Somerset House. Sir G. S. Mackensie has 

 noticed this :— " I conceive," he says, * no dependence can be 

 placed on the thermometric observations made in the garden of the 

 Horticultural Society. It is some time since I pointed out to Pro- 

 fessor Lindley the defects of the apparatus. Instead of the thermo- 

 meter being placed in the shade of a wall, it is exposed near the 

 ground under a wooden roof, which absorbs the direct rays of the 

 sun and radiates heat to the instrument. Thus the indications of 



