754 
PROFESSOR 0. REYNOLDS ON CERTAIN DIMENSIONAL 
a portion of the traced curve g' Ti coincides with a portion of c cl. The effect of the 
superposition is shown in the figure, e b and eg' cl being the portions of the curves 
which overlap. O' is the new position of 0. 
It will at once be seen that O' M is the logarithm of the ratio of corresponding 
abscissae, while O' N is the logarithm of the corresponding ordinates. 
In this particular case 
O' N= ’7 — log. 5 
0 / M=-77=log. 5-9. 
These numbers differ somewhat from those given by Tables X. and XI., and the 
difference is very suggestive. The absolute agreement of the curves shows that the 
difference is not owing to experimental inaccuracy, and it will be seen on comparing 
the results next given that the difference (5 and 5*9) is owing to a difference in the 
temperature in the two instruments. If the temperatures had been the same we 
should have had the same ratio for the corresponding ordinates as for the abscissae; 
but a difference in the temperature would alter all the ordinates in a certain ratio 
without affecting the abscissae. 
The difference O' N —O' M='07=log 1*175 gives the ratio in which the differences 
of pressure are affected by a difference in temperature. This, according to the law 
that the results are proportional to the square roots of the differences of temperature, 
would be equivalent to a difference of 21° in the temperature of the water. This 
difference did not exist, hence there must have been a difference, owing to the greater 
thickness or to the different nature of the meerschaum plate. 
The size of the woodcut does not admit the points indicating the actual experiments 
being shown, but these are shown in the larger figures, Plates 48 and 49. 
Stucco plate No. 2. 
29. These facts will be better understood after examining the experiments on a second 
stucco plate. The trial of this plate was owing to an accident to the diffusiometer 
containing stucco plate No. 1. The diffusiometer was thereupon refitted with another 
plate similar to No. 1; but the old tin plates were replaced by new bright ones, and 
the new india-rubber rings were somewhat thicker than the old ones. 
