94 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



the escapement-wire, so that at each semi-revolution of the 

 shaft the wire, if too fast, will strike the pallet, and be re- 

 tarded till the pendulum swings clear of it, the motion of 

 the collar being thus governed by the pendulum. In the 

 clock in the author's house, the arc of vibration does not 

 exceed half a centimeter on each side of the vertical. As 

 to the compensation, the zinc and platinum compensation 

 at first adopted have been discarded, and mercury and glass 

 substituted with the most satisfactory results. 



Higgs has described a simple motor for preserving a 

 pendulum in vibration during the course of an experiment. 

 The pendulum is suspended through the coil of a Siemens 

 galvanoscope, and automatically so breaks and closes the 

 circuit that the deflection of the needle attached to the sus- 

 pending rod upward or downward keeps up the motion. 



2. Of Liquids. 



Amagat has published in full his memoir on the compres- 

 sibility of liquids, in which he especially considers the effect 

 of temperature and of pressure upon the coefficient of com- 

 pressibility. The apparatus consisted of a hollow iron rec- 

 tangular base containing mercury, on the top of which was 

 a pump to give the pressure (the piston being worked by a 

 screw), a manometer closed at top and surrounded by a cyl- 

 inder containing water, and a piezometer, the latter consist- 

 ing of a bulb tube to contain the liquid to be examined, the 

 open end being inverted and cemented into an opening in 

 the iron base, and the bulb extending up into a chamber 

 with glass sides, containing water at any desired tempera- 

 ture. The results, so far as the question of temperature is 

 concerned, are in complete accord witli theory, the coeffi- 

 cients increasing with the temperature. With regard to 

 the influence of pressure, the author finds that within wide 

 limits of pressure, and quite independently of the variation 

 due to temperature, the coefficient always diminishes as the 

 pressure increases. Thus for ether at 100, the coefficient 

 from 8 to 14 atmospheres was 0.0005C0, and at 30 to 36 at- 

 mospheres it was 0.000474, while at 13.7 it was 0.0001G8 

 and 0.000152 respectively. 



Millar has made some experiments on the relative density 

 of liquid and solid iron. He finds that pieces of pig-iron 



