286 THE OBSERVATORY AT ST. MARTIN, ISLE JESUS, C. E. 



feet from the ground, and liave occupied tlie same position for some 

 years, being placed free from radiation, and carefully shaded from the 

 sun and rain. 



The Psychrometer, consists of the dry and wet bulb thermometers, 

 the scales of which are coincident, and have been carefully read 

 together. There is also a Saussures' hygrometer. In winter the wet 

 muslin is supplanted by a thin covering of ice which requires frequent 

 renewal. 



Eor solar radiation a maximum Eutherford's thermometer is used, 

 vdth the bulb kept blackened with Indian ink ; the tube is shaded 

 by a piece of glass blackened also with Indian ink, which prevents 

 the index from adhering to either the tube or the mercury, as is 

 often the case when not shaded. 



Terrestrial radiation is indicated by a spirit thermometer of Eu- 

 therford, which is placed in the focus of a parabolic mirror, 6 inches 

 in diameter and of 100 inches focus. 



Drosometer or dew measurer. — One is of copper, like a funnel, the 

 inside of which has been exposed to the flame of a lamp and has been 

 coated with lamp black ; the other is a shallow tin dish painted black 

 and ten inches in diameter. 



Rain-gage. — The reservoir is thirteen inches in diameter, and is 

 placed 20 feet above the soil. It is self- registering, and is attached 

 to the anemometer and shews the beginning and ending of the rain 

 and the amount of precipitation in inches on the surface. 



The Snow-gage presents 200 square inches of surface, and is placed 

 in an open space. The surface of the snow requires to be lightly 

 levelled, before taking the depth, which is recorded in inches. A 

 tin tube, 3 inches in diameter aud 10 inches long, is used for obtain- 

 ing snow for the purpose of reducing the amount to the relative 

 amount of water. The tin tube fits in another vessel of tin of the 

 same diameter, and the snow is easily reduced and measured. 



The Evaporator exposes a surface of 100 inches ; and is carefully 

 shaded from sun and rain. It is made of zinc and a glass scale, 

 graduated in inches and lOths, is well secured in front of it, 

 a strip of the metal being removed the glass scale supplies its 

 place, so that the amount evaporated can be easily read off. Its 

 place is supplied in winter by a pair of scales, upon one of which is 

 placed a disc of ice, and the amount of evaporation from_ the surface 

 is estimated by being very accurately weighed. 



The Ozonometers are Schonbien's and Moffat's. The solutioa 



