500 Dr. W. Marcet on the Function of Respiration at [Apr. 24, 



that station was intense, as my tent was erected in a hollow, and the 

 sand became so hot in the afternoon that the hand conld not bear being- 

 kept in contact with it. 



The mean of twenty-two readings of a Fortin barometer, by Casella, 

 compared with the observations of Professor Smyth, taken at sea near 

 the coast of Teneriffe, in 1856, at a similar time of the year, or nearly 

 so, gave an altitude of 7,090 feet above the sea for that station. The 

 stations in the Alps where my former experiments had been carried 

 out, and corresponding in altitude with my Guajara station on 

 Teneriffe, were the Eiffel (8,425 feet) and St. Bernard (8,115 feet), 

 these however being rather over 1,000 feet higher. 



The highest of my principal stations on Teneriffe was that of Alta 

 Yista, where Mr. Piazzi Smyth also resided in 1856. This was near 

 the summit of the Peak on a small "plateau," occurring in a break 

 between lava streams. This station faced an easterly aspect ; in the 

 evening a cold westerly wind often blew, sweeping down from the 

 summit and feeling exceedingly chilly. The altitude of this station 

 according to Piazzi Smyth, is 10,702 feet. An accident to my 

 barometer just before leaving Guajara put an end to barometrical 

 readings, but an observation as to the temperature of boiling water 

 at Alta Yista gave me exactly the height as determined by Professor 

 Smyth. This altitude compares well with that of St. Theodule, 

 10,899 feet, one of my stations in the Alps. 



The N.E. trade winds cause a belt of clouds to hover over the 

 island ; I entered this layer of fog at an altitude of 3,200 feet, and 

 left it at 5,500 feet, its thickness amounting therefore to 2,300 feet. 

 My stations on the Peak were of course above the clouds ; on one 

 occasion only did I see them from Alfca Vista make an irruption into 

 the wide plateau at the foot of the peak between 6,000 and 7,000 feet 

 high, but they soon withdrew. 



2nd, Temperature. — The sky was cloudless till the last day, when 

 a few light clouds appeared overhead, and the sun being nearly 

 vertical at noon, in July, its direct heat was very great, although 

 the air was much less warm in the shade ; on the other hand the cold 

 w.'^ very sharp at night. While the sandy surface of the soil was so 

 hot a*;, two or three o'clock in the afternoon, that the hand could not 

 bear to be pressed against it, water left outside the tent in a bucket 

 or in plates was on several occasions found frozen next morning just 

 before sunrise. I had no black bulb thermometer in vacuo for 

 observing the solar radiation, but Professor Smyth found on the 

 summit of Mount Guajara over 180° P., with such an instrument by 

 half-past nine o'clock in the morning, and he concludes that on 

 August 4th, the black bulb temperature in the sun must have been 

 212°*4, the thermometer reading in the shade being only 60°, thus 

 leaving the enormous quantity of 152° for the effect of sunshine at 



