S44 Scientific Proceedings, Royal Dublin Society. 
Such, briefly, was the state of the inquiry, when Professor 
Preston—working with the Rowland Grating of the Royal Uni- 
versity—brought his first research before this Society towards the 
close of 1897. (‘* Radiation Phenomena in a Strong Magnetic 
Field,” Trans. R. D.S., vol. vi., Ser. 11., 1898, p. 385.) 
Members of this Society who were present on that occasion, will 
recollect that they were treated to no second-hand account of the 
phenomena, but were shown—a feat not before attempted—the 
triplication and quadruplication of the lines of cadmium and zine 
by means of photographs projected on the screen. 
In this communication, Professor Preston not only showed that 
he had attained a higher degree of resolution of the lines than had 
up to this been accomplished, but he was able to announce the 
existence of quartet and sextet forms for the first time. In his 
paper he seeks for explanation of the quartet variation from the 
normal triplet, and the fact that the difference of wave-length 
introduced -by the magnetic force is not proportional generally to 
the square of the wave-length (as the simple theory seemed to 
suggest) was forced upon him at this early stage of his work. 
Although these matters were laid before the Royal Dublin 
Society in December, 1897, Professor Preston can lay still earlier 
claim to these observations, as appears from a short communication 
to Nature in November of the same year. (Nature, vol. 57, 
1898, p. 173.) 
The second memoir on the subject appeared in the Transactions 
of the Royal Dublin Society for June, 1899 (vol. vi., Ser. 1., 
pp. 7 ef seg.), having been read by Professor Preston in January 
of that year. 
He here offers an explanation of the quartet form analogous 
to Professor Fitz Gerald’s suggestion that the ionic orbits will 
vibrate with definite period about their position of rest in the 
magnetic field, and records the observation that, for corresponding 
lines of the natural groups or series of Keyser and Runge, the 
theoretic condition obtains. 
He further, in this communication, suggests a law which 
apparently involves the far-reaching conclusion that structural 
features 1n common are possessed by chemically related atoms. 
Although such a conclusion commends itself for other well-known 
reasons, so direct a proof as is involved in ‘ Preston’s Law,” had 
a a ee 
