962 
MR. O. REYNOLDS ON THE MOTION OF WATER AND OF 
readings entered in the notes referred to one or other limb of the gauge, care having 
been taken to indicate which. 
In the Tables III., IV., and V. of results appended, the noted readings are given 
and the letters r, 1 , and b signify whether the reading was on the right or left limb, or 
the sum of the readings on both limbs. 
The readings marked l and r are reduced by the correction for the difference in 
the size of the limbs as well as the coefficient for the particular fluid in the gauge. 
Thus it was found with the mercury tube that when the left limb had moved 
through 39 divisions on the scale the right had moved through 41, so that to obtain 
the sum of these readings the readings on the left, or those marked l, had to be 
multiplied by 2 - 05 and those on the right by 1'95. 
With the bisulphide of carbon gauge, 11 divisions on the left caused 9 on the 
right, so that the correction for the reading on the left was 1'8 and on the right 2‘2. 
29. Comparison of the pressure gauges .—The pressures as marked by the gauges 
were reduced to the same standard by comparing the gauges; thus ‘25 of the left limb 
of the mercury corresponded with 24 inches on both limbs of the bisulphide. There¬ 
fore to reduce the readings of the bisulphide of carbon to the same scale as those of 
the mercury they were multiplied by 
•25 x 20-5 
24 
= 0-0213 
This brought the readings of pressure to the same standard, i.e., T^ooth of an inch 
of mercury, but these were further reduced by the factor 0’00032 to bring them to 
metres of water. 
As it was convenient for the sake of comparison to obtain the differences of pressure 
per unit length of the pipe, the pressures in metres of water have been divided by 
1\524, the length in metres between the gauge holes, and these reductions are 
included in the tables of results in the column headed i. 
From the discharges as measured by the various gauges having been reduced to 
cubic centimetres, the mean velocity of the water was found by dividing by the area 
of the section of the pipe. 
30. Sections and diameters of the pipes. —The areas were obtained by carefully 
measuring the diameters by means of fitting brass plugs into the pipes and then 
measuring the plugs. In this way the diameters were found to be— 
Diameter, No. 4 pipe, '242 inch, 6*15 millims. 
„ No. 5 pipe, '498 inch, 127 millims. 
These gave the areas of the sections— 
Section, No. 4 pipe, 29'7 square millims. 
,, No. 5 pipe, 125 square millims. 
