SI 8 BIETEOROLOGY. 



over an opening made in it, fitting to the hollow part of the cone. 

 Immediately under this table is placed a small stove of sheet-iron, 

 ahput 8 inches in diameter, is made double, the space of about 1 inch 

 being left between the two chambers ; and I have found this plan very 

 good to effect a good insulation by keeping the whole of the appa- 

 ratus warm and dry. Charcoal is used as fuel, and is, I think, prefer- 

 able to a lamp. A coating of suet or tallow is applied to the glass 

 cones or pillars. Care must be taken not to rub or polish the collect- 

 ing apparatus as it seems to deteriorate its power of collecting and 

 retaining atmospheric electricity ; and I have found that its collecting 

 powers increase with its age. Suspended from these cross arms hang 

 i\\e electrometers. 1. BenneV s electroscope of gold leaves ; this scarcely 

 needs a description. 2. Voltas' electromder No. 1, consisting of two 

 straws 2 Frencb inches long ; a very fine copper wire passes through 

 these straws which are suspended from the cross arms. This elec- 

 trometer is furnished with an ivory scale, the old French inch being 

 divided in 24 parts, each being 1° ; this forms the standard scale for 

 the amount of tension. 3. Voltas' electrometer No. 2 is similar to the 

 No. 1, but the straws are five times the weight of No. 1, so that one 

 degree of Voltas' No. 2 is equal to five of No"". 1. Henhfs electrometer 

 is a straw suspended and furnished with a small pith ball ; each of 

 the degrees of Henly's is equal to 100° of No. 1 of Voltas. These 

 electrometers are all suspended from the cross arms. A discharging 

 apparatus, furnished with a long glass handle, measures the length 

 of the spark, and serves also as a conductor to carry the electricity 

 collected to the earth, and is also connected by a chain and iron rod 

 passing outside of the observatory for about 20 yards and buried under 

 ground. 



Various forms of distinguisJiers are used to distinguish the kinds of 

 electricity. The Voltas electrometers may be rendered self-registering 

 with great facility by the photographic process, by placing a piece of 

 the photographic paper behind the straws and throwing the light of 

 a good lens upon them ; the expansion is easily depicted and serves 

 well for a night register. There is also a Peltier's electrometer, and 

 another form of electrometer, consisting of two gold leaves suspended 

 to a rod of copper 2 feet long ; the upper end being furnished with a 

 wire box, in which is kept burning some rotten wood, {touch-wood.) 



The anemomeier consists of a direction shaft and a velocity shaft; id 

 the top of the direction shaft is placed the vane, which is 18 feet in 

 length. The shaft is made of three pieces, to insure lightness and 

 more eaej motion ; each piece is connected bj means of small iron- 

 toothed wheels. The two shafts are six feet apart, and work on cross 

 arms from a mast firmly fixed in the ground. The vane passes some 

 6 or 8 feet above the velocity shaft, and does not in any way interfere 

 with the other movements. The lower extremities of these shafts are 

 all furnished with steel points, whicli work on an iron plate or a piece 

 of flint, and pass through the roof of the observatory ; the openings 

 being protected by tin parapluies fixed to the shaft and revolving 

 with them. Near the lower extremity is placed a tootheii wheel § 

 inches in diameter, which is connected to another wheel of the same 

 diameter, which carries upon its axis a wooden disc 13 inches in dia- 



