34 Prof. Marcet on the Variations of the Temperature 
teract the noxious effects of sulphuretted hydrogen, when such 
is found to exist distributed through the atmosperic air.* 
To Captain Washington, R.N. Gustav Biscuor. 
Researches on the Variations which take place at certain periods 
of the day in the Temperature of the Lower Strata of the 
Atmosphere. By Professor Marcur, Transmitted by the 
Author.} 
Ir appears, from researches now of old standing, and dating, 
for the most part, from the end of the last century, that the 
relations which exist between the™temperature of the strata 
of air adjoining the earth, are subject to variations depending 
either on the state of the sky, or on the time of the day at 
which the observation is made. Our countryman, M. Mare 
Auguste Pictet, was the first who, in 1770, studied with care 
the variations of two thermometers, one of which was placed 
5 feet above the ground, the other at a height of 75 feet. He 
remarked, that when the weather was calm and clear, the 
temperature of these two thermometers agreed about two hours 
after sunrise, and from that time throughout the whole day, 
the thermometer at 5 feet above the ground was constantly 
higher than that at 75 feet ; that the two thermometers again 
corresponded some time after sunset, and from that time till 
eleven o'clock in the evening, the lower thermometer under- 
went a relative depression of about 23° of the centigrade 
seale.{ Pictet adds, that when the sky was completely over- 
cast, or during the prevalence of a strong wind, the difference 
between the temperature of the two thermometers was scarce- 
* We are informed by letter from Dr Stanger, dated off the Niger, that 
Dr M‘William, who has carefully examined the sea-water near the mouths 
of all the rivers from time to time, has not yet been able to find any trace of 
sulphuretted hydrogen in freshly taken water ; but when the waters had been 
kept a few days in corked bottles, it was twice very evident,—Hdit. of Hdin. 
Phil. Jowrnal. 
+ Mémoires de la Societé de Physique et d’ Histoire Naturelle de Genéve, 
T. viii. 2me partie. 
{ Throughout this memoir the indications are given according to the cen- 
tigrade thermometer, unless the contrary is expressly mentioned. 
