i 3 o THE POPULAR SCIENCE MONTHLY. 



lie ; while the very instruments used by Davy, and which I first saw 

 figured in the pages of the journal just mentioned, are the identical 

 and familiar instruments with which my lectures in London are now 

 illustrated. 



Another point brought more or less home to me in those early 

 days was the injury inflicted on the learner by bad scientific exposition. 

 It does more than the negative damage of withholding instruction. 



CU if o 



It daunts the young mind, and saps the motive power of self-reliance. 

 This I had experienced ; and the essays referred to had this special 

 value for me, that they not only instructed me, but gave me faith in 

 my own capacity to be instructed. Since those days I have written 

 books myself, and in doing so have tried to remember, and to act on 

 the remembrance, that the labor spent in logically ordering one's 

 thoughts, and in saying what one has to say clearly and correctly, is 

 labor well bestowed. 



The position assumed at the outset has, I think, been now made 

 good. Glasgow in my case cast its bread iipon the waters, and lo ! 

 it has returned after many days. Of the nutritive value of the return 

 it is not for me to speak; for it may well have been soured by for- 

 tuitous ferments, mixed by the world's tainted atmosphere with the 

 first pure leaven derived from the pages of The Practical Mechanics 

 and Engineer's Magazine. 



The figure of speech here employed will become more intelligible 

 as we proceed; for it is my desire and intention to spend the com- 

 ing hour in speaking to you about ferments, not in a metaphorical, but 

 in a real sense. Proper treatment is, I am persuaded, the only thing 

 needed to make the subject both pleasant and profitable to you. For 

 our knowledge of fermentation, and of the ground it covers, has aug- 

 mented surprisingly of late, while every fresh accession to that knowl- 

 edge strengthens the hope that its final issues will be of incalculable 

 advantage to mankind. 



One of the most remarkable characteristics of the age in which we 

 live is its desire and tendency to connect itself organically with pre- 

 ceding ages to ascertain how the state of things that now is came to 

 be what it is. And the more earnestly and profoundly this problem 

 is studied, the more clearly comes into view the vast and varied debt 

 which the world of to-day owes to that fore-world in which man, by 

 skill, valor, and well-directed strength, first replenished and subdued 

 the earth. Our prehistoric fathers may have been savages, but they 

 were clever and observant ones. They founded agriculture by the 

 discovery and development of seeds whose origin is now unknown. 

 They tamed and harnessed their animal antagonists, and sent them 

 clown to us as ministers, instead of rivals, in the fight for life. Later 

 on, when the claims of luxury added themselves to those of necessity, 

 we find the same spirit of invention at work. We have no historic 

 account of the first brewer, but we glean from history that his art 



