1894.] Viscosity of Water as shown by Microrheometer. 259 



the charging pressure was connected to these points and observations 

 taken, when the exciting current for the field magnets of the dynamo 

 and the charging current to the pipe were practically the same as in 

 a previous set of experiments, for which the charging volts were 

 known. Both sets of experiments are shown in the table. The dis- 

 turbance of the worms was again very distinct, and they appeared, 

 on reaching the surface, to set their bodies parallel to the pipe, or 

 along an equipotential line. 



The experiments, as a whole, show conclusively that, under very 

 different conditions of weather and amount of moisture in the soil, it 

 is possible to produce a fall of potential amounting to 25 per cent, of 

 the whole pressure in the supply between points on the surface of the 

 ground 4 ft. apart, a distance which most horses stand over, and, 

 further, that, although the connexion of such points by a conducting 

 body naturally reduces this potential difference, yet, when this con- 

 ductor has about the resistance of a horse (say 400 ohms), sufficient 

 current will pass to give a severe shock. 



It is hoped that, when opportunity serves, these experiments may 

 "be extended to the case of pipes buried to greater depths, and to 

 observe whether any difference is produced by the use of a steady, in 

 place of an alternating pressure. 



VI. ''On the Viscosity of Water as determined by Mr. J. B. 

 Hannay by means of his Microrheometer." By ROBERT 

 E. BARNETT, A.R.C.S. Communicated by Professor T. E. 

 THORPE, F.R.S. Received May 6, 1894. 



In a paper entitled " On the Microrheometer," published in the 

 * Philosophical Transactions ' for 1879, Vol. 170, p. 275, Mr. J. B. 

 Hannay describes an apparatus with which he made measurements 

 of the rate of flow of water, and of some aqueous saline solutions 

 through a capillary tube, and he deduces from the observations cer- 

 tain relations between the chemical nature of the salt dissolved, and 

 its effect on the rate of flow of water. 



Inasmuch as Mr. Hannay furnishes us with details of the dimen- 

 sions of his apparatus, I have, at Professor Thorpe's suggestion, 

 transformed his relative numbers into absolute measure of viscosity 

 in order to compare his results with those of other workers. The 

 data given are as follows : 



Diameter of capillary tube = 0'0938 mm. 



Length = 21 mm. 



Capacity of glass bulb = 4*0530 c.c. 



The time of flow was measured by a stop-watch, and each number 

 recorded was the mean of ten observations. 



s 2 



