Notes and Comments. 299 
so-called standard remain of a constant length? It certainly 
will change by temperature, it probably will change by age (that 
is, by the rearrangement or settling down of its component 
molecules), and I am not sure if it does not change according to 
the azimuth in which it is used. At all events, you must see 
that it is a very impractical standard—impractical because, if, 
for example, any one of you went to Mars or Jupiter, and the 
people there asked you what was your standard of measure, you 
could not tell them, you could not reproduce it, and you would 
feel very foolish. Whereas, if you told any capable physicist in 
Mars or Jupiter that you used some natural invariable standard, 
such as the wave-length of the D line of sodium vapour, he 
would be able to reproduce your yard or your inch, provided 
that you could tell him how many of such wave-lengths there 
were in your yard or your inch, and your standard would be 
availabe anywhere in the universe where sodium is found.’ In 
this way Clerk Maxwell impressed great principles upon his 
students. Sir David adds, ‘We all laughed before we under- 
stood; then some of us understood and remembered.’ The vote 
of thanks to the President was proposed by Lord Kelvin, whom 
to see and hear was alone worth the journey to the Midlands. 
THE GROWTH OF BOTANICAL SCIENCE. 
In the course of his Presidential Address to the Botanical Sec- 
tion, Professor J. B. Farmer mentioned that the problems that 
confronted them as botanists were far more numerous and far 
more complex than formerly. They were attached to a science 
that was rapidly growing, and this advance was carrying with it 
a process of corresponding differentiatior. In rating highly the 
value of maintaining a physiological atutude of mind towards 
the phenomena presented by the vegetable kingdom, one was 
mainly influenced by the logical necessity which such a position 
carried with it of constantly attempting to analyse their pro- 
blems, as far as might be possible, into their chemical and 
physical components. He believed it was only by the help of 
the elder branches of science—chemistry and physics—that the 
accurate formulation, to say nothing of the final solution, of the 
problems in which they were engaged would be analysed. 
THE HISTORY OF THE EARTE, 
To the Geological Section, Prof. J. W. Gregory delivered a 
scholarly Address in which many interesting topics were touched 
upon. After referring to the geology of the inner earth, he said 
1907 September 1. 
