Mr. Meikle on a Syphon Hydrometer. 



167 



Fahr. for instance, it must either be brought to such stand- 

 ard, or a small correction will be required : but every hydro- 

 meter requires a similar adjustment of far greater magnitude. 

 In this instrument it may in general be neglected. 



In the foregoing description I have, for greater simplicity, 

 supposed the axes of the four legs to lie all in one plane ; but 



F? 



o 



V_J 



they may be arranged differ- pj„ 2. 



ently, and on some accounts, ^— -^ 



perhaps, with advantage*. As 



the liquids in pouring back from 



the instrument will be apt to )p 



mix, this would be prevented if 



a small part of the upper double 



end of the tubes were somewhat 



bent, so as to stand a little above 



all the tubes when they are held 



horizontally. 



By help of an instrument of 

 this kind very wide between the 

 middle legs (as in fig. 2.), so as 

 to admit of each pair being put 

 into a separate bath, the grand 

 question regarding the tempera- 

 ture at which water possesses the maximum density, might be 

 decided with greater certainty than by any other method 

 which, so far as I know, has been employed for the purpose f. 

 Thus if water were put into both sides, we could find at what 

 temperature the effective column is always the shorter of the 

 two ; or, having found two temperatures at which the columns 

 are equal, the mean between these would be very nearly the 

 number sought. It might also be obtained by interpolating 

 between several irregular observations lying on different sides 

 of the maximum. 



Could scales be obtained which would neither alter by mois- 

 ture nor by a small change of temperature, these might be 

 used within the baths, and the process of course would be so 

 much the simpler. I presume, various sorts of wood, if kept 

 dry, would undergo no change in length between 32° and 50° ; 

 and might, therefore, be safely used as scales outside the baths. 

 An apparatus might easily be contrived, which, being placed 



* That part for instance containing the one liquid may be put on one 

 side of a scale, and the other part on the other side of the same scale. 

 This was the first form which I adopted. It is less liable to mix the liquids. 



f The method employed by MM. Dulong and Petit for determining the 

 expansion of mercury, might, I have no doubt, be employed in solving this 

 question ; but I presume the double syphon will be more easily managed. 



outside, 



