8 Transactions of the 



thermograph in the next storey above ; the intermediate storey 

 being used as an office. 



The construction of the various instruments was explained by 

 means of numerous and well-executed drawings, without which 

 it would be impossible to give more than a brief and general 

 description.* 



The velocity of the wind is registered by means of four copper 

 cups placed at the extremities of two horizontal cross bars, four 

 feet long, which turn a vertical rod. This rod is connected by 

 wheel-work, and another rod, with a metallic pencil, which 

 draws lines (more or less rapidly, according to the force of the 

 wind) on a sheet of paper kept travelling, at a uniform rate, in 

 contact with it, by means of clock machinery. In consequence 

 of the wind meeting with a greater resistance from the concave 

 than from the convex surface of the cups, these always turn in 

 the same direction. Still the motion is much retarded by the 

 resistance of the convex surface, and it is calculated that the 

 rate at which the cups move is one-third of the rate of the 

 wind. A line on the register-paper, representing fifty miles 

 passed over by the wind, is drawn when the cups have revolved 

 7000 times. Immediately such a line has been drawn, the 

 pencil begins to mark another line. Sometimes in the course of 

 twenty-four hours, only one or two such lines are drawn ; some- 

 times as many as twenty or more. The highest register in one 

 day, was on February 3, 1869, when more than twenty-three such 

 lines were drawn, representing 11 72 miles. The greatest velocity 

 registered in one how was 73 miles, on September 12, 1869. At 

 this rate the cups would revolve nearly three times in a second. 



The direction of the wind is shown by means of a heavy 

 vane, which is kept turned towards the point from which the 

 wind blows, by two fans similar to those which are used to 

 keep the sails of a mill towards the wind. The direction is 

 registered on the same paper as the velocity, and in nearly the 

 same manner. 



The variations in the barometer and thermometer are re- 

 gistered by the aid of photography, which, while -it successfully 

 and beautifully accomplishes the object required, does not, in 

 the least degree, interfere with the free action of the quicksilver. 

 Sheets of waxed paper, each 19 inches long and 6 inches broad, 

 are prepared with iodide of silver, so as to be very sensitive to 

 the action of light. Two of these sheets are placed round a 

 vertical cylinder, which is inclosed in a sort of wooden case to 



* Most of these were drawn on a very large scale from the figures in the 

 Report of the Meteorological Committee for 1S6S, in which a minute description 

 wiU be found. 



