372 Miscellaneous Intelligence. 



mercury into the funnel tube, and with a horse-hair or fine wiie 

 remove the air, so that the column may be continuous ; then 

 pour in so much of this prepared mercury as will fully displace 

 the mercury that was boiled in the tube; afterwards remove the 

 funnel tube, and put the barometer to its proper use. It will be 

 found to stand exactly at the same height as before in the same 

 circumstances ; and if the mercury be now boiled in the tube 

 none of those bubbles will appear which arose on the first boil- 

 ing ; care being taken throughout, that the inner surface of the 

 tube has not been exposed to the air. 



Perhaps an easier mode of making the same experiment is to 

 make the barometer terminate at top in a bulb, which will hold 

 more mercury than is required to fill the tube : then when it is 

 boiled it need only be placed upright in a basin of common 

 mercury, and when inclined the mercury will enter and replace 

 that which was boiled in the instrument ; the results will be as 

 above. 



An experiment proving the same thing may be made still more 

 easily thus : fill a mercurial thermometer and boil it well ; then 

 heat it till nearly all the mercury is expelled, but preserve its 

 open extremity under common mercury : the latter metal will 

 enter as the instrument cools, and behave in every respect as 

 the well-boiled mercury did. — Giornale di Fisica, vi. 20. 



10. Maximum Density of Water. — The maximum density of 

 water is a point which, though frequently spoken of and sought 

 after, has never been accurately ascertained. Mr. J. Crichton, 

 of Glasgow, who has lately been engaged in determining the 

 specific gravity of certain fluids by means of adjusted balls of 

 glass, was so satisfied with the simplicity and accuracy of the 

 method, that he determined to apply it to the investigation of the 

 point above mentioned, and after much careful experiment has 

 fixed it with apparently great accuracy at 42. 3°F. 



In a first experiment with these balls, one, which was just 

 poised in water at SS*^, had the same property near 51°; this 

 gave 42° for the point of greatest density, supposing the expan- 

 sion equal for equal differences of temperature above and below 

 the maximum density. 



Many precautions are required in these kind of experiments : 

 whilst cooling the water it should be kept as still as possible, 

 agitation charging it with air; the presence of air-bubbles 

 should be very carefully attended to, for when one happens to 

 adhere to the ball, the experiment is vitiated. An uniform tem- 

 perature should be attended to in every part of the mass of 

 water, and the pbsence of currents ascertained. The delicacy 

 of the ball itself may be imagined, when it is understood that 

 the removal of the 6000th part of a grain, or as little as could 

 possibly be ground off, has been too much. At first spherical 

 balls were used, but afterwards they were made in the form of 



