402 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



and no loss is experienced as is the case witli the old-fashioned regulator, 

 where the balls move perceptibly before the throttle valve is changed. 



This governor riins at a high speed, and has a short screw-rod at the top 

 which connects with the valve in the chest below ; there is also another 

 nut for altering the tension of the spiral spring, S. These nuts enable the 

 speed of the engine to be easily controlled ; for by running the nut, U, up 

 or down on the rod, V, the spring is relaxed, or set up so that more cen- 

 trifugal force is required to afiect the balls, and the speed of the engine 

 increases to make up this force ; when the spring is relaxed, the reverse 

 occurs. The governor-valve, in the chest before spoken of, is also changed 

 in its position in a manner not necessary to describe at present. 



Horology. 



The Chairman opened the subject for the evening's discussion by remark- 

 ing that the word Horology is derived from the Latin horologium, and 

 originally from two Greek words meaning "to tell the hour." Among the 

 ancients the art of measuring time was quite imperfect. The oldest instru- 

 ment we have any account of, was the Clepsydra. This name is derived 

 from two Greek words signifying " the stealing away of water," and has 

 reference to the gradual and almost imperceptible manner in which the 

 water moves in the Clepsydra. There were several varieties of this water 

 clock used in Chaldea, India, and China. The most common device con- 

 sisted of a vessel, on the side of which was marked at regular intervals, the 

 number of the hour. Into this a stream of water of uniform size and velo- 

 city was discharged, and as the vessel filled the height of the water in it 

 indicated the time. It is apparent that there was some difficulty in securing 

 uniformity to the inflowing stream ; this was doubtless obviated by having 

 the stream issue from an orifice, near the bottom of a second vessel, which 

 was kept constantly full to overflowing. If the hours were marked by the 

 emptying of a fuU'vessel by means of an orifice at the bottom, the gradua- 

 tion would require constantly increasing intervals from the top to the bot- 

 tom, the height of water in the vessel being directly as the square of the 

 velocity of discharge. The sun-dial, used at a later period, had the advan- 

 tage of correctness, but is available only during that small portion of time, 

 when it receives the direct rays of the sun. There are many forms of 

 dials, that in most common use and in our day occasionally placed in 

 pleasure groimds and gardens, is a horizontal disk on which is a perpen- 

 dicular gnomon in a line parallel with the axis of the earth. 



Another rude method of measuring time came into use after the invention 

 of candles ; it was a simple graduation of the candle into spaces corres- 

 ponding with the length consumed in a given period. The hour or sand- 

 glass is another old device, and is preferable to the Clepsydra because the 

 pressure of sand at the orifice of discharge does not depend on its height 

 as is the case with water. It consists of a frame holding two glass cones 

 placed apex to apex in the same right line, and having a small passage 

 connecting them. It contains sand sufficient to fill one cone, which is dis- 

 charged by gravity into the cone below, in a given time. A very neat 

 little sand-glass requiring about three minutes for the discharge of its 

 sand is in common use to regulate the time for boiling eggs. All these 



