282 THE OBSERVATORY AT ST. MARTIN, ISLE JESTJS, C. E 



a series of wheels moved by a spindle, rotates a dial inside the build- 

 ing marked with the usual points of the compass. Another staff, 

 about 30 feet high, contains the anemometer, or measurer of the force 

 of the wind, which, by a like arrangement of apparatus, is made to 

 register its changes inside. The last pole, 20 feet in height, contains 

 the rain guage, the contents of which are conducted by tubing also 

 into the interior of the building, in which, by a very ingenious con- 

 trivance, the commencement and ending of a fall of rain are self- 

 marked. 



At the door entrance on the right side is a screened place, exposed 

 to the north, on which the thermometer and wet bulb thermometer 

 are placed, four feet from the surface of the earth. A similar apart- 

 ment on the left contains the scales with which experiments are 

 conducted throughout the winter to ascertain the proportional evapo_ 

 ration of ice. 



On entering the door, in the centre of the apartment is a transit 

 instrument in situ, for the convenience of using which openings are 

 made in the roof, usually kept closed by traps. This apparatus is not 

 the most perfect of its kind, but is amply adequate for all its uses. 

 On the left is a clock, the works of which, by means of a wheel, are 

 made (while itself keeps proper time,) to move slips of paper along 

 little railways, on which the anemometer by dots registers the velo- 

 city of the wind ; the rain guage, the commencement and end of 

 showers ; and the wind vane, the continually shifting currents of 

 wind. This is effected by a pencil, kept applied by a spring to a 

 piece of paper on the dial previously alluded to, and as, by the clock- 

 Avork, the dial and the two previously mentioned slips of paper move 

 at the rate of one inch per hour, so it is easy to determine, in the 

 most accurate manner, the direction and force of the wind at any 

 hour of the day, or any period of the hour. "With the exception 

 of the clock, the whole of this miniature railvray work, with all its 

 apparatus, wheels, &c., &c., is the work of Dr. Small wood's own hands, 

 and exhibits, on his part, a mechanical talent of the highest order. 



At the extreme end of the room is a table, beneath which is an ar- 

 rangement for a heating apparatus, and on which is the four arm 

 conductor previously alluded to. • To the two lateral and front arms 

 hang, respectively, two of Volta's electrometers, and one of Bennet's, 

 while beneath the knob on the anterior, there is a discharging appa- 

 ratus, with an index playing over a graduated scale, to measure 

 during thunder storms the force of the electric fluid, by the length of 



