1866. | Hofmann and Modern Chemistry. 71 
who witnessed with pleasure and instruction the well-devised and 
successfully performed experiments. Even H.M. the Queen was 
pleased to listen to some of Dr. Hofmann’s lectures, and he repeat- 
edly had the honour of delivering short chemical courses to the 
Court at Windsor Castle and at Osborne. 
Nothing can show more completely Dr. Hofmann’s power of ren- 
dering an abstract subject pleasing than his lecture delivered at the 
Royal Institution on the 7th of last April “On the Combining 
Power of Atoms.” In this lecture, which has been printed with 
wood-cuts, Dr. Hofmann introduced an entirely new mode of illus- 
trating the subject. “I will,” he says, “on this occasion, with your 
permission, select my illustration from the most delightful of games, 
croquet.” He makes croquet balls represent the atom, and the 
atoms of different elements are distinguished by different colours. 
He adds another mechanical contrivance to indicate the combining 
power of the atoms; this is effected by screwing into the balls 
metallic pegs, by which they can also be joined so as to rear 
mechanical structures in illustration of the atomic edifices to be 
illustrated. “Thus the hydrogen and chlorine atoms, which are 
univalent atoms, have each one arm, representing one combining or 
attraction unit; the atom of oxygen, a bivalent atom, has two, re- 
presenting two attraction units; while the nitrogen and carbon 
atoms, respectively trivalent and quadrivalent, are provided with 
three and fowr arms, indicating the three and four combining units 
respectively distinguishing the atoms.” By fixing those balls to- 
gether in the order in which experiment has proved to us they 
combine, visible representations of the compounds which result from 
their combination are produced. In this way instruction is afforded 
by reaching the mind through the eye, which would never so 
readily have found ingress through the portal of the ear. 
From the first Dr. Hofmann fully appreciated his task. He 
knew that to make the College of Chemistry successful and to esta- 
blish for himself a name in England, his teaching must be made to 
tend to practical results. While he never flinched from impressing 
theory on the minds of his pupils, he made them all practical 
workers. They learned as much by what they saw passing before 
them as by their own actual manipulation. Dr. Hofmann has been 
particularly and truly characterized by his power not only of getting 
into the minds of his students the utmost amount of knowledge, but 
by his kindly encouragement, getting the most out of them for the 
advancement of science. As an example of this, during the last few 
years Dr. Hofmann has been entirely engaged in the elucidation of 
the chemistry of the new coal-tar colours which have attracted so 
much attention. This industry has in a great measure emanated 
from the Royal College of Chemistry ; most of those who first en- 
gaged in this new branch of applied chemistry, Messrs. Perkin, 
