1879.] Various Altitudes on the Island and Peak of Teneriffe. 499 



and full of a titered solution of barium hydrate, in addition to which 

 there were a number of empty bottles of the same size. The bottles 

 holding the alkaline solution were carefully corked and the corks 

 sealed with paraffin. I must also allude to two strong deal boards 

 or rocking-boards, 6 feet in length and supplied with two iron sockets 

 midway between the two ends ; the sockets fitted upon an iron bar 

 raised a few inches high on a firm wooden stand. Two square open 

 wooden boxes were made to fasten at one end of each board respec- 

 tively, and could be filled with stones or sand up to a given weight. 

 The use of these boards will be explained in the course of the present 

 communication. 



In addition to the above apparatus I carried with me a balance and 

 everything required for determining the moisture expired from the 

 lungs. My experimental baggage used in the Alps was also included, 

 together with every requisite for camping out on the Peak for about 

 three weeks. 



My Chamounix guide, Edouard Cupelin, who has accompanied me 

 for the last ten years in the Alps, and is thoroughly used to the mani- 

 pulations connected with my experiments, came out with me to 

 Teneriffe. He not only assisted me most effectually, but also sub- 

 mitted himself to experiment. 



We arrived at the Island of Teneriffe on the 25th of June last, and 

 after landing at Santa Cruz, proceeded at once to Puerto de Orotava, 

 at the foot of the Peak. Three principal stations were selected, two 

 at different altitudes on the Peak, and one at the seaside ; while from 

 the highest station instruments could be carried to the foot of the 

 terminal cone, and also to the summit of the Peak 12,200 feet above 

 the sea, where I proposed making a few experiments. 



We remained eleven days at the lowest station on the Peak, at an 

 altitude of 7,090 feet, and ten days at the higher station 10,700 feet 

 above the sea. 



The characters of the stations bearing on my experiments were : — 



1. The topographical position and atmospheric pressure. 



2. The temperature of the air. 



3. The hygrometric state of the atmosphere. 



1st. The position and atmospheric pressure. My lowest station on the 

 Peak, that of Gruajara, was situated on a sandy plateau at the foot of 

 Mount Gruajara, known from Professor Piazzi Smyth having esta- 

 blished an astronomical station at the summit in 1856. The moun- 

 tain rose 1,800 feet above my station in the S.W., while in the 

 opposite direction for 200 or 300 yards, there spread a patch of white 

 sand mixed with clay, and baked by the sun. Beyond that could be 

 seen a bank of blocks of lava tumbled over each other, which formed 

 the edge of an upper undulating level reaching the foot of the actual 

 Peak at a distance of two or three miles. The heat of the sun at 



