The size of the animals varies greatly, from forms a few millimetres in length to Gigantorhynchus gigas, which measures from 10 to 65 cms. The adults live in great numbers in the alimentary canal of some vertebrate, usually fish, the larvae are as a rule encysted in the body cavity of some invertebrate, most often an insect or crustacean, more rarely a small fish.
(If the molecules of air at normal temperature and pressure were arranged in cubical order, the edge of each cube would be about 2.9 X I o - ' cms.; the average diameter of a molecule in air is 2.8X Io - 8 cms.) Further and very important evidence as to the nature of the gaseous state of matter is provided by the experiments of Joule and Kelvin.
C =183,900 cms. per sec.
Thus if a fork Ut 3 = 256 is used, the length of pipe for the fundamental at o° C. is about 33,000/4X256 =33 cms. If a fork Solo= 768 is used the pipe resounds to it according to the mode of the first overtone.
Perot and C. Fabry, employing their interferometer methods, have compared the wave-length of the red cadmium line with the standard metre in Paris and found it to be equal to 6438.4696 A, the observations being taken in dry air at 18° C and at a pressure of 76 cms. (g = 980.665).
The disks were 10 cms. in diam., and nearly 2 cms. thick, plated with copper to a thickness of 2 mm.
The chief difficulty, as usual, was the determination of the gradient, which depended on a difference of potential of the order of 20 microvolts between two junctions inserted in small holes 2 cms. apart in a bar 1 .
5' cms. in diameter.
The Wire Had A Length Of 760 Cms., And The Potential Difference On Its Terminals Was Nearly 30 Volts.