382 Eighth Annual KEroRT of the 



a complete revolution. The recording pen (which is attached to 

 the same carriage with that of the direction register), traverses 

 the length of the cylinder in 24 hours, and thus leaves upon the 

 tracing sheet a spiral line, every complete turn indicating 100 

 kilometers of wind. 



In addition to the hundredth meter contact, the anemometer is 

 also provided with a second contact, which is made at every revo- 

 lution of the anemometer wheel, and the circuit thus established 

 is transmitted to a Richard's anemo-cinemograph, devised to regis- 

 ter the details of the wind movement, and to show its maximum 

 force during gusts. In this instrument an electro-magnet and 

 mechanism operated by it^ raise the pen arm of the cinemograpli 

 about one-thirty-second of an inch at every co'utact; while a clock- 

 work depresses the arm at a rate i)roportionate to its distance 

 from the zero position. With a given wind velocity, therefore, the 

 arm takes a i^osition such that the rate at which it is being raised 

 by the anemometer contacts exactly balances ^hat at which it is 

 being depressed by the clock movement; and in this position is 

 quickly changed to correspond with variations in the wind veloc- 

 ity. As in the other instruments_, the height of the pen above 

 the zero point is registered upon a band of paper carried by a uni- 

 formly rotating cylinder. As the cinemograp'h is needed chiefly 

 to record the force of violent gusts, a mechanism has been devised 

 which puts it in operation only when the wind velocity exceeds 30 

 miles per hour. 



A Richard's anemometer for measuring the force of vertical air 

 currents (or their vertical components), is also placed on the tower 

 of McGraw hall. This anemometer has four inclined blades or 

 fans, rotating about a vertical axis, upward and downward cur- 

 rents turning it in opposite directions. Two sets of contacts are 

 provided, one of which is operated by upward and the other by 

 downward currents. The number of turns of the anemometer 

 is registered upon a C3'liuder in the manner employed for recording 

 horizontal velocities^ excepting that the cylinder is made to turn 

 to the right by downward currents, and in the opposite direction 

 by upward currents. The movement of the cylinder is also ten 

 limes more rapid than in the case of the horizontal register for 

 winds of the same velocity. 



