TRANSACTIONS OF THE SECTIONS. 35 



Thus the plus sign preponderates, indicating greater -warmth above, during 

 the day and night, in January, February, October, November, and December, and 

 during the night throughout the year. 



A second thermometer, properly protected from radiation, was placed in the 

 middle of the year 1869 at the height of 50 feet; and since then its readings have 

 been regularly taken. The mean monthly temperatures of the air, at 50 feet height, 

 ■were found to differ from those at 4 feet, as follows : — 



At g"" A.M. At Noon. AtS'^p.ir. At 9'' p.m. 



18C9, October +02 -6-5 +07 +1-5 



November 0-6 +0-o 0-8 1-4 



December 00 0-.3 0-5 0-5 



1870, January 1-1 +0-3 7 0-9 



Februarv +01 -0-3 +03 0-5 



March .". -0-3 1-2 -07 0-7 



April 09 2-2 1-7 1'4 



May 2-4 3-6 2 8 1-1 



June 2-4 3-8 3-1 1-1 



July 1-8 2-9 2-8 1-2 



Aiigust —1-7 -2-7 -20 +1-7 



_ Thus we have the unexpected result that the mean monthly temperature of the 

 air at 22 feet and at 50 feet height is higher during the evening and night-hours 

 throughout the year than at the height of 4 feet, and also higher, night and day, 

 during the winter months. By selecting those days with a sky covered by dense 

 clouds, it was found that there was on such days no difterence between the tem- 

 perature at 4 feet, 22 feet, and 50 feet height. At the height of 50 feet, in the 

 summer months, the temperature during the day was frequently 6 and 7 degrees 

 lower than that at 4 feet, and at night 5 or G degi-ees higher. 



On a New EIecfro-3fagnetic Anemometer, and the mode of -using it in Regis- 

 tering the Velocity and Pressure of the Wind. By Jomsr J. Hall, 



After describing at some length the difficulties attending the use of the present 

 forms of anemometrical apparatus, arising from the fact that few houses are built 

 with any means of access to the roof, also from the interference of trees and undu- 

 latory surfaces of land, &c., and having showed the practical results that would be 

 derived from the use of electricity, the author proceeded to describe the apparatus 

 devised (and exhibited) by him. One of the main objects for which it is intended 

 is the determination of interval or hourly velocities. The following is a brief 

 risume of its principles and construction : — 



The anemometer consists of two parts, viz. Velocity apparatus and Registering 

 apparatus. 



The first consists of a set of Robinson's hemispherical cups, which communicate 

 their motion downwards into a brass box, where it is reduced in angular velocity 

 and causes a contact-disk or commutator (in which two platinum contact-pins are 

 fixed equidistant from one another) to revolve in tenths of a mile. An insulated 

 metallic lever, having a platinum working face, stands on each side of the disk so 

 that, upon the completion of every -^ mile, one or other of the contact-pins comes 

 into contact with the two levers, thus imiting them and completing the circuit. The 

 levers, which are jointed at their opposite ends, are raised a few degrees (of circles, 

 whose radii they represent), and then fall back to their nonnal position, ready to 

 be taken up by the next pin, and so on. 



The Recording apparatus consists of a train of wheels and pinions working in a 

 frame or between two brass plates, tlie arbors of which project through a 

 dial-plate (whereon the circles and figures are engraved), and carry the hands. 

 These wheels are di-iven by a weight attached to a line which is wound round a 

 ban-el ; and a locking pin-disk (the pinion of which works in the first wheel) is re- 

 leased at every contact of the cup apparatus by an electro-magnet, which unlocks 

 the pin-disk and allows the first hand to advance -g^ mile on the graduated dial 

 by n jump similar to the minute-hand in remontoire clocks. 



3* 



