Mr. Meikle on an improved Syphon-Hydrometer. 259 



straight parallel legs; and though alittlecomplex,it has obviously 

 the property of being free from the effects of capillary action. 

 In the Edinburgh Philosophical Journal for January 1827, a me- 

 thod is given for applying the simple syphon to the same pur- 

 pose, but which is not so entirely unaffected by capillary ac- 

 tion. The same method, however, appears to be still suscep- 

 tible of considerable improvement, so as to be rendered one of 

 the simplest, and at the same time furnishing a pretty accurate 

 instrument What I would suggest, as likely to render a simple 

 glass syphon very convenient as a hydrometer, is merely to 

 put a small hole in its upper or bent part. On immersing each 

 leg of such a syphon in a separate liquor, a portion of the air 

 escapes through the hole, and allows the liquids to rise in the 

 tubes to the level of their cisterns. If we now apply the finger 

 to the hole, and raise the instrument, I need scarcely say, not 

 wholly out of the fluids, the liquors will be raised in the tubes 

 by the pressure of the atmosphere, so as to form columns ele- 

 vated to heights above their respective cisterns inversely pro- 

 portional to their specific gravities. For the weights of the 

 two columns must obviously be equal ; each being the difference 

 between the pressure of the atmosphere and that of the in- 

 cluded air. 



If the tube be pretty wide, the effect of capillary action may 

 in most cases be neglected: so that, the one column being 

 water, we divide its length by that of the other liquid, and ob- 

 tain a quotient which is the specific gravity of the latter. But 

 the effect of capillary action may be easily obviated altogether, 

 by holding the syphon at two different heights, and noting the 

 corresponding columns. Thus if at one height we have a co- 

 lumn of water =W, and at another height = w; while the 

 corresponding columns of another fluid are respectively A 

 and a ; the specific gravity of the latter, freed from capillary 

 action, is 



A-a ' 



For, if x be the capillary part of the column of water, and y 

 that of the other fluid, we should correct the columns for ca- 

 pillary action, by diminishing them respectively by x and y ; 

 whence the specific gravity becomes 



W — x w—x ~W—w 



A-a 



We thus obtain the specific gravity free from capillary action, 

 by dividing the difference of the columns of water by the dif- 

 ference of those of the other fluid. The greater these differences 



2 L 2 can 



