8 PRESIDENTIAL ADDBESS. 



a new weapon wherewith we can force Nature to surrender more 

 of her secrets to us, as it must be of great advantage in the manu- 

 facture of lenses, since it is ahvays easier to make a low power 

 than a high one. No doubt, lenses will be cut on more perfect 

 curves now that the index of refraction is increased. 



In the practical use of a lens, a low power is always more 

 readily used and corrected, besides being considered more satis- 

 factory. Then it has the great advantage of not being so easily 

 damaged. It is for us to make the best use we can of these new 

 powers placed in our hands, and thus to help forward the science 

 of microscopy. We ought not to despise the old methods and pro- 

 cesses, but we ought to improve on them by grafting the new on 

 the old, and bind them into a homogeneous mass by the use of 

 our brains. 



Microscopical study has the advantage of suiting every calibre 

 of mind and taste, and to all it offers fresh knowledge and nume- 

 rous untrodden paths, which are open to any student who feels a 

 desire to enter into original research on his own account, and thus 

 we can all make our lives useful and assist to build up the scienti- 

 fic knowledge of the world, and act up to the motto printed on 

 the cover of our Journal, that " knowledge is not given us to keep, 

 but to impart. Its worth is lost in concealment." 



Formation of Pearls. — In oysters aged four years — which 

 are judged by the shells, weight, and appearance — the best pearls 

 are found. The shell, like the pearl, is formed by the secretion 

 of the animal, and is composed of animal matter and lime. The 

 iridescent hues on the inside of the shell are occasioned by the 

 edges of the thin, wavy, concentric layers overlapping one 

 another and reflecting the light. The minute furrows, containing 

 translucent carbonate of lime, produce a series of more or less 

 brilliant colours, according to the angle at which the light falls 

 upon them. Occasionally, some of the finest pearls are found 

 loose in the shell. As many as one hundred pearls have been 

 found in one oyster, but are of litde or no value. The pearls of 

 the young oyster are yellow, and in the older oyster are of a 

 pinkish hue. — 7?u//. U.S. Fish Comni. 



