108 NEGRETTI AND ZAMBRA, HOLBORN VIADUCT, B.C., 



and forwards as the wind alters the position of the vane. To this rack a pencil, 

 #, is attached, which marks the direction of the wind on a ruled paper, placed 

 horizontally beneath, and so adjusted as to progress at the rate of half an inch 

 per hour, by means of a simple contrivance connecting it with a clock, which 

 carries the registering paper forward by one of the wheels working into a rack 

 attached to the frame. The paper is shown in the illustration upon the table 

 of the instrument. 



The pressure plate, F, for ascertaining the force of the wind, is one foot 

 square, placed immediately beneath the vane ; it is supported by light bars, 

 running horizontally on friction rollers, and communicating with springs, 

 1, 2, 3, so that the plate, when affected by the pressure of the wind, acts upon 

 them, and they transfer such action to a copper chain passing down the 

 interior of the direction tube, and over a pulley at the bottom. A light copper 

 wire connects this chain with a spring lever, y y, carrying a pencil which 

 records the pressure upon the paper below. Mr. Osier prefers a spring to any 

 other means for ascertaining the force of the wind, because it is of the highest 

 importance to have as little matter in motion as possible, otherwise the 

 momentum acquired will cause the pressure plate to give very erroneous 

 indications. The pressure plate is as light as is consistent with strength. 

 It is kept before the wind by the vane, and is urged out by three or more 

 springs, so that with light winds one only is compressed, and two, or more, 

 according to the strength of the wind. 



The pluviometer is placed on the right in the figure, PP being the plane of 

 the roof of the building. The rain funnel, R, exposes an area of about two 

 hundred square inches. The water collected in it is conveyed by a tube through 

 the roof of the building into a glass vessel, (?, so adjusted and graduated as to 

 indicate a quarter of an inch of rain for every two hundred square inches of 

 surface, i.e., 50 cubic inches. is supported by spiral springs, b b, which are 

 compressed by the accumulating rain. A glass tube, open at both ends, is 

 cemented into the bottom of G, and over it is placed a larger one closed at the 

 top like a bell glass. The smaller tube thus forms the long leg of a syphon, 

 and the larger tube acts as the short leg. The water, having risen to the level 

 of the top of the inner tube, drops over into a little copper tilt, t, in the globe, 

 S, beneath the reservoir. This tilt is divided into two equal partitions, and 

 placed upon an axis not exactly balanced, but so that one end or the other pre- 

 ponderates. The water drops into the end of the tilt which happens to be 

 uppermost, and when quite full it falls over, throwing the water into the globe, 

 S, from which it flows away by the waste pipe. In this way an imperfect 

 vacuum is produced in the globe, quite sufficient to produce a draught in the 



