324 Lord Rayleigh : Investigations in Capillarity. 



ends being ground to a plane, and carefully levelled. Ten 

 drops, following one another at intervals of about 50 seconds, 

 were usually weighed together. As to the interval, sufficient 

 time must be allowed for the normal formation of the drop, 

 but the fact that evaporation is usually in progress forbids 

 too great a prolongation. The accuracy attained was not so 

 great as had been hoped for. Successive collections, made 

 without disturbance, gave indeed closely accordant weights 

 (often to one-thousandth part), but repetitions after cleaning 

 and remounting indicated discrepancies amounting to one- 

 half per cent., or even to one per cent. The cause of these 

 minor variations has not been fully traced ; but the results 

 recorded, being the mean of several experiments, must be free 

 from serious error. Attention may be called to tubes 11 and 

 12 of nearly the same (external) diameter. Of these 11 was 

 plugged so as to leave only a small bore, the end being 

 carefully ground flat. It will be seen that the difference in 

 the weights of the drops was but small. 



Again, No. 10 was of barometer-tubing, having a com- 

 paratively small bore, which accounts for the slightly 

 diminished weight of the drop. The other tubes were thin- 

 walled. In all cases care was taken that the cylindrical 

 part of the tube, though clean, should remain unwetted, a 

 condition which precluded the use of diameters much less 

 than those recorded. 



Glass. 



Metal. 



1 



•088 



•0375 



15 



•400 



•1446 



2 



•134 



•0526 



16 



"450 



•1662 



3 



•191 



0712 



17 



■500 



•1882 



4 



•200 



•0755 



18 



•530 



•2023 



5 



•256 



•0923 



19 



•550 



•2130 



6 



•354 



•1151 



20 



•559 



•2167 



7 



•383 



•1362 



21 



•580 



•2256 



8 



•406 



•1461 



22 



•597 



•2295 



9 



•459 



•1703 



23 



•621 



•2389 



10 



•465 



•1698 



24 



•640 



•2454 



11 



•521 



•1969 



25 



-680 



•2510 



12 



•523 



•2023 



26 



•730 



•2531 



13 



•566 



•2210 



27 



•SCO 



•2509 



14 



•584 



•2339 









second column are the external 

 inches (one inch = 2*54 cm.), while 



The numbers in the 

 diameters measured in 



the third column gives the weight in grams of a single drop, 

 corrected for temperature to 15° C, upon the supposition 



