the Maximum Density of Water, 



43 



apparatus of Dr. Hope did not however appear to us to pre- 

 sent the method in a form calculated to give results of great 

 accuracy;- and hence we have found it necessary to devise a 

 new instrument combining all the theoretical advantages with 

 the requisite facilities for exact observation. 



Our instrument is i-epresented in the 

 accompanying sketch, a a are two up- 

 right vessels of tinned iron, each 4i feet 

 high and 6 inches in diameter : they are 

 connected at the bottom by means of a 

 brass pipe b, furnished with an accurately 

 wrought stop-cock. This pipe is altogether 

 6 inches long, and enters 1 inch within 

 each vessel. When the stop-cock is opened 

 a clear passage of 1 inch diameter through- 

 out forms a communication between the 

 vessels. A rectangular trough of tinned 

 iron, c, 6 inches long, 1 inch broad, and 



1 inch deep, forms a communication be- 

 tween the tops of the vessels. In the 

 middle of this trough there is a slide, by 

 means of which the motion of a current 

 along the trough can be stopped when 

 requisite. 



The vessels were supported in two places by means of the 

 wooden brackets dd, and in order to prevent the greater than 

 desired effect of the atmosphere in raising or depressing their 

 temperature, they were completely covered with haybands. 

 During the experiments the instrument was placed upon a 

 tripod stool resting upon a suppoi't quite independent of the 

 floor of the laboratory, in order to keep it entirely free from 

 vibration. 



Now if the t\\ o vessels be filled with water and made to 

 communicate with one another by opening the stop-cock and 

 removing the slide, it is evident that a current will tend to 

 How througli the trough coiuiecting the tops of the vessels, 

 if the density of the water in one of the vessels be in the least 

 degree greater tluui that of the water in the other vessel. 

 Although the changes in density are very minute near the 

 maximum point, the extreme mobility of fluids led us to 

 expect that we might in this way arrive at an exact and in- 

 controvertible result. 



The thermometers employed by us were of extreme accu- 

 racy, having been calibrated throughout their whole length, 

 ami their delicacy was such as to indicate a change of tempe- 

 rature considerably less than ii'juth of a degree Fahreidieit. 



