460 



Miscellaneous Intelligence. 



while its dispersive power is only 0.026 compared to water as 

 0.035. Thus if a sapphire is ground in the same tool which v.'ill 

 form a lens of glass of the ^\ inch focus, it will come out about 

 the -j^-jj inch focus ; being almost double the power of the glass in 

 linear amplification, and more than double in superficial ; in which 

 latter mode of estimation the powers of the glass and sapphire may 

 be rated at 360,000 to 1,000,000. The faint blue tinge of the sap- 

 phire is not felt in thin small lenses formed of this substance, which 

 thus come next in order to diamond ones, and form an excellent 

 pis aller for those who cannot come at the latter. Many of our 

 first microscopists are already in possession of them, and have 

 honoured them with their unqualified approbation. 



There is a property possessed by small single lenses formed by 

 precious stones, which is worthy of being commented on : viz. They 

 can be burnished fast into brass rings, and thus safely cleaned and 

 removed at pleasure from one setting to another. The cohesion of 

 glass is too slight to permit this operation, during which it is 

 almost sure to burst into shivers. — C. R. G. 



15. On a Method of Securing and Preserving the Rowing Pins 

 in Boats. — Dear Sir, — To remove a petty inconvenience of hourly 

 occurrence, by some simple contrivance, is often productive of a 

 greater mass of advantage than an invention of greater splendour, 

 and of apparently more extensive utility. 



In the accompanying drawing, you have a plan for preserving 

 that indispensable requisite in a boat, the towels, or rowing pins ; 

 the loss of which is not only very teasing, but often productive of 

 serious inconveniences; while the practice of stealing them from 

 each other forms a constant source of petty depredations, leading 

 to perpetual quarrels among seamen in harbours. He who has 

 been detained the better part of a day in the island of Sky, till half 



