356 The Observatory at St. Martin. 



Rutherford, 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-guage. — 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-guage 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 and 10 inches long, is 

 used for obtaining 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 care- 

 fully 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 diso 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 solutioi? 

 consists of one drachm of starch, boiled in one ounce of distilled 

 water, to which is added when cold 10 grains of the Iodide of 

 Potassium — this is spread on sized paper which is found to an- 

 swer better than bibulous or unsized paper, for the solution is more 

 equally distributed over the surface, whereas on bibulous paper 

 it is very difficult to spread the solution equally. It is cut into 

 slips of about 3 inches long and 5 inches wide — having been 

 previously dried in the dark it is also requisite, to keep it dry and 

 free from light. When required one of these slips is placed 5 

 Teet from the ground and shaded from the sun and rain, — another 

 of these slips of ozone paper is elevated and exposed at an altitude 

 of 80 feet, for the purpose of comparison. It is also well to place 

 slips of this prepared paper in the vicinity of any vegetables, which 

 may be affected with disease, for instance during the prevalence 

 of the potatoe rot. 



