146 SCIENCE SKETCHES. 
“A man cannot be professor of zodlogy on one 
day and of chemistry on the next, and do good 
work in both. As inaconcert all are musicians, — 
one plays one instrument, and one another, but 
none all in perfection.” 
~ “You cannot do without one specialty. You 
must have some base-line to measure the work and 
attainments of others. For a general view of the 
subject, study the history of the sciences. Broad 
knowledge of all Nature has been the possession 
of no naturalist except Humboldt, and general 
relations constituted his specialty.” 
~““Select such subjects that your pupils cannot 
walk out without seeing them. Train your pupils 
to be observers, and have them provided with the 
specimens about which you speak. If you can 
find nothing better, take a house-fly or a cricket, 
and let each one hold a specimen and examine it 
as you talk.” 
“Jn 1847 I gave an address at Newton, Mass., 
before a Teachers’ Institute conducted by Horace 
Mann. My subject was grasshoppers. I passed 
around a large jar of these insects, and made every 
teacher take one and hold it while I was speaking. 
If any one dropped the insect, I stopped till he 
picked it up. This was at that time a great inno- 
vation, and excited much laughter and derision. 
There can be no true progress in the teaching 
of natural science until such methods become 
general.” 
“There is no part of the country where in the 
summer you cannot get a sufficient supply of the 
best specimens. Teach your children to bring 
