Mr. C. Tomlinson on the Cohesion-Figures of Liquids, 187 



water has been poured into the glass, it must be allowed to come 

 to rest before the drop is deposited upon its surface. 



It is desirable to have three or four glasses in regular work ; 

 these should be of the same size and shape. The form of glass 

 used by me is a conical tumbler about 3| inches in diameter at 

 the mouth. The water need not be distilled, provided it be 

 clean. The glass rods must be wiped after every experiment, 

 and washed in caustic potash solution. The washing, &c. (which 

 has been complained of as troublesome) really gives little or no 

 trouble, provided suitable arrangements be made for it. My 

 plan is to keep two glasses full of the potash solution, one a 

 beaker, and the other a small Phillips's glass. When an ob- 

 servation is complete, the contents of the tumbler are emptied 

 into a waste-pan, in such a way that little or none of the oil (if 

 an oil-film be present) shall adhere to the glass. The glass is 

 then rinsed out with a little water, filled up with potash solution, 

 and emptied back into the potash vessel, taking care in pouring 

 to turn the glass round so as to wash every part of the edge ; 

 for to this the oil is apt to cling, and soil the fresh water that is 

 next poured in. The glass rods should be kept in the Phillips's 

 jar; and when one is taken out for an experiment it must be 

 wiped dry on a clean duster, then dipped into the oil and 

 allowed to drain, so that one and only one drop shall be depo- 

 sited on the water. The rod is then wiped on another duster 

 and returned to the potash solution. The pipettes used for 

 ethers, &c. should also be kept clean; a number standing 

 upright in a cylindrical glass jar is a useful arrangement. 



With respect to temperature, results are most consistent when 

 it is pretty constant, such as the mean temperature of the air in 

 summer, and the warmth of an ordinary room in winter. I 

 shall, however, have more to say on this subject presently. 



I am encouraged to believe that these details will not be 

 thought trivial, when I call to mind that the minute details con- 

 tained in my first instructor in chemistry (' Chemical Manipu- 

 lation') were the production of as high a scientific genius as 

 this country has probably ever produced. 



I have stated above that the glasses used in these experiments 

 present a surface of water 3| inches in diameter. Now, as ad- 

 hesion plays a considerable part in the production of cohesion- 

 figures, it may be asked, what would be the effect of varying 

 the adhesion by enlarging or contracting the surface-area ? 



In order to throw light on this question I selected four vessels 

 — A, a small thick shallow foot-glass, into which was poured 

 2 oz. of water ; B, a large dinner plate, containing 4 ozs. of water ; 

 C, my usual conical tumbler, containing 8 ozs. of water; and D, 

 an evaporating dish, containing 16 oz. of water. Their surface- 



