448 Mr. D. J. Blaikley on the 
doubtless, to errors of observation and partly to an assumption 
of the absolute correctness of Laplace's formula, the theory in 
the application of which is that the excess of pressure in the 
wave above the barometric pressure of the air is infinitely 
small. 
Experiments on the velocity of sound may be classed as 
open-air experiments and laboratory experiments ; and I 
venture to think that the latter offer advantages which cannot 
be enjoyed in open-air work. The usual method in the open 
air has been for an observer at a distance from a gun to note 
the time which elapses between the flash and the hearing of 
the report ; but even when the actual record of the time is 
aided by electrical or other apparatus, some difficulties and 
sources of error remain. For instance, the accurate registra- 
tion of temperature and moisture is difficult, especially when 
the sound-wave passes at various heights above the earth' 
surface, as is the case when th( 
two hills separated by a valley. 
Many of these gun-fire determinations were critically exa- 
mined by Le Roux*, and an estimated correction made for 
errors in temperature, the readings having been in all proba- 
bility too high for air some metres above the ground. 
Midway in character between open-air and laboratory expe- 
riments stand those of Regnault, carried out in gas- and water- 
mains ; one of his reasons for choosing this method being the 
facility afforded by these tubes for the accurate observation 
of temperature and moisture. Passing by his work for the 
moment, we may note the laboratory method employed 
by Kundt, and also Le Roux's method, the latter giving 
330*7 metres at 0°C. Kundt's method consists in its best 
form in the use of two glass tubes connected by a smaller 
tube or rod of glass, wood, or metal, this connecting-rod being 
clamped in certain positions to establish nodes, and its free 
vibrating ends being fitted with pistons working in the large 
tubes. The waves are excited by friction in the vibrating rod 
and transmitted therefrom to the air or other gas in the tubes, 
and the successive half-wave lengths are registered by the 
positions assumed by lycopodium dust during the vibration. 
By using tubes of different diameters he obtained the results 
shown in Table L, and came to the conclusion that the velo- 
city observed in his largest tube was not appreciably different 
from the velocity in free air. He appears, however, to June 
experienced some difficulty in the determination of pitch, 
owing to the evanescent character of the sound. The intensity 
* Ann. de C'himie, ser. 4, tom. xii. Nov. 1SG7. 
