400 Quedionsfor Solution relating to Meteorologyy 



on the deck, and that at the summit of the mast, will indicate 

 "Very nearly the same degree. The experiment, nevertheless, is 

 not the less deserving of attention. In the estimation of a pru- 

 dent natural philosopher, there is always an immense distance 

 between the result of a conjecture and that of an observation. 



Expeditious Method of determining Mean Temperatures in 

 Equinoctial Countries. — In our climates, the stratum of the 

 earth which undergoes neither diurnal nor annual variations of 

 temperature, is situated at a great distance from the surface of 

 the ground. But such is not the case in equinoctial regions ; 

 for, according to the observations of M. Boussingault, nothing 

 more is necessary than merely to sink a thermometer to the depth 

 of yd of a metre (about 1 foot), in order to make it indicate 

 constantly the same degree, or very nearly so. Travellers, 

 therefore, may determine very exactly the mean temperature of 

 all the places they visit between the tropics, either in plains or 

 in mountains, by having the precaution to furnish themselves 

 with a miner''s piercer, with which it is easy, in a few minutes, 

 to pierce a hole in the ground of the required depth. It will 

 be found that the action of this instrument on rocks and on the 

 soil, occasions a development of heat, and the observer should 

 always wait till that be entirely dissipated before he commence 

 his experiments. It is likewise necessary that the air in the 

 bole should not be renewed during the whole time of their 

 continuance. A soft substance, such as pasteboard, covered 

 with a large stone, will form a sufficient preventive. The ther- 

 mometer ought to have a string attached to it, by means of 

 which it may again be drawn up. 



The observations of M. Boussingault, of which Ave have avail- 

 ed ourselves, in order to recommend perforations to the trifling 

 depth of a foot, as conducting very expeditiously to the deter- 

 mination of mean temperatures in all intertropical countries, 

 have been made in sheltered places, in the ground, under In- 

 dian huts, and under mere sheds. In these situations, the soil 

 was sheltered from the direct warmth produced by absorption of 

 the so^ar light, from nocturnal radiation, and infiltration of 

 rains. Every one trying the experiment should place himself 

 in similar circumstances, for there can be no doubt that in the 

 open air, and in places remote from shelter, it would be needs- 



