MECHANICS AND USEFUL ARTS. 117 



slide away from it. The whale line is forked or split, and each part 

 thereof is rove through a pulley or sheave attached to the flukes, and 

 is thence led and attached to the socket or staff which is firmly fixed 

 to the point. 



When the harpoon is thrown and enters the whale, and strain is 

 brought upon the line, the flukes spread out and take firm hold in the 

 blubber, detaching themselves by such motion from the point. The 

 pulleys, or sheaves they carry, are now fixed in the whale, and the 

 strain upon the line passing through them forces the shank and its 

 point to slide between them, penetrating deeply into the whale. 



Gas Regulator. Three patents have been granted for three sev- 

 eral modifications of this instrument. The instrument consists of an 

 enlarged chamber in the service pipe, where it enters the consumer's 

 building, and is generally placed near the Gas Company's meter. 

 Each of the modified regulators is designed merely to equalize the 

 size of the flame, while the number of burners is varied. This en- 

 larged chamber in the pipe has a valve, which controls the amount of 

 gas going to the burners, and thus divides the chamber into two com- 

 partments one being on the side towards the street main, and the 

 other on the side towards the burners. The valve is at one end of a 

 small scale beam or lever, and counterpoised at the other by an in- 

 verted cup in a vessel of mercury. It is easily seen that if we vary 

 the pressure on the external surface, of the inverted cup, or on the in- 

 ternal surface, we increase or diminish the opening of the valve, and 

 thus admit more or less gas. In the first of these devices patented, the 

 internal part of the inverted cup communicates with the side or com- 

 partment of the chamber towards the burners ; in the second, it com- 

 municates with that towards the street main ; and in the third, the 

 construction is such that it communicates with both at the same time, 

 and thus modifies and controls the amount of s;as received through 



o O 



the valve in three several ways. 



Geometrical Measurement. A geometrical instrument has been 

 patented, which is termed by the inventor a center-square for finding 

 the center of a circle, designed for the use of mechanics. The gene- 

 ral principle upon which the instrument is based is well known to 

 geometricians, viz : that if two tangents (or straight lines touching 

 the circumference of a circle) be extended until they intersect each 

 other, a straight line bisecting the angle between them will pass 

 through the center of the circle. The instrument consists of two arms, 

 placed together at right angles to each other, in the manner of a car- 

 penter's square, but of equal thickness, and having their surfaces 

 " flush ; " upon the upper surface of which arms a straight ruler is 

 fixed at its end in such a manner as to have one of its edges at the 

 inner angular point of the arms, and that edge extending midway be- 

 tween them, or bisecting the angle between them. This ruler can be 

 braced firmly by a bar running across between the extreme ends of 

 the arms. If the mechanic wishes to find the center of a circular 

 wheel he places the instrument upon it, with the two arms both resting 

 against its circumference, in which position the edge of the ruler will 



