35 4j Professor Marcet upon the Variations in the 



of M. Fictet, and of the English naturalist Six, undertaken to- 

 wards the close of the last century. After demonstrating that 

 the observations of these philosophers are not sufficient in a 

 satisfactory manner to resolve the different inquiries which pre- 

 sent themselves, the author proceeds to the description of the 

 apparatus which he himself employed in the prosecution of the 

 subject. 



This apparatus consists in a mast 114? feet high, composed 

 of two spars of fir, accurately connected with each other; di- 

 verse precautions being taken that they should not be broken 

 or overturned by the violence of the wind. It was placed in 

 the most favourable situation for experiments of this kind, that 

 is to say, in the midst of a great field, at a considerable distance 

 from all habitations. The author adjusted, at the distance of 

 every ten feet throughout the whole length of the mast, hori- 

 zontal pieces of wood, to the extremity of which was attached 

 a little pulley, by means of which the thermometers might be 

 made to ascend and descend. The thermometers employed 

 had their bulbs well covered with some good non-conducting 

 substance, so that it might be certain their temperature did 

 not vary during the time of their descent. Accurate notation 

 was made, at the moment of every observation, of the meteoro- 

 logical condition of the atmosphere, and, in particular, of the 

 indications of the hygrometer and of the ethrioscope. 



The principal object which the author had in view in his re- 

 searches may be regarded as a solution of the four following- 

 questions : — Isty To what extent the increase of temperature, 

 which has been observed in proportion to elevation, during 

 certain periods of the day, is influenced by the condition of 

 the sky, and the agitation of the air.? To determine, 2dl^, 

 in a precise way, at what periods of the day this increase of 

 temperature becomes perceptible ; if it remain constant, or if 

 it have a tendency to increase during the night ? Sdli/, Does 

 the limit of elevation, at which this increase of temperature 

 ceases, remain constant, or does it vary according to the meteo- 

 rological state of the atmosphere ? And, 4^/1/3/, Whether the in- 

 crease of temperature, as well as the limit of its elevation, re- 

 main constant, or vary according t3 the different seasons of the 

 year .'' 



