236 Scientific Intelligence. [Sept. 



X. Graduation of Glass Titles. 



I have received the following query on this subject from an 

 anonymous correspondent: — 



" On trying your method of graduating glass measures of 

 capacity, I met with a difficulty against which your directions do 

 not provide, and which renders the previous accuracy of operation 

 useless. It is this: — A measure of mercury in the tube or measure 

 to be graduated will have a more convex surface than anv body 

 which the. glass is intended hereafter to measure, and the degree of 

 convexity differs for different bores. Hence if we mark the highest 

 point of the surface, the measure will be too large; if the lower, 

 or edge, too small. How then do you determine this matter ? The 

 thickness of the tube is one source of uncertainty. I have made 

 several measures of thick tube, with a lamp and bellows ; but find 

 the widened part, or rim, is very subject to break off, when cold, of 

 its own accord. Pray can you inform me how the tubes themselves 

 are fiist made, and where?" 



My rule, and I believe the method generally followed, is always 

 to consider the uppermost part of the mercury as the place against 

 which the mark on the tube is to be placed : and if this rule is 

 always adhered to, no sensible error will ever be committed. Thick 

 tubes do not answer so well as those that are finer, because they are 

 apt to break of themselves without any assignable cause ; so that if 

 we employ them we run the risk of being under the necessity very 

 frequently of renewing our labour. The glass tubes (which are 

 drawn at all the crystal glass-houses) are not annealed, which no 

 doubt is the reason of their being so brittle. I do not know the 

 reason why this process is neglected with respect to them, though 

 probably there is a good one. 



XI. Electroxide. 



To the same intelligent correspondent I am indebted for the 

 following curious fact: — ■ 



" I have lately seen a beautiful electroxide on a white-washed 

 wall, produced by lightning dispersing a large copper bell-wire, in 

 passing through a house at Cirencester, about seven o'clock on 

 Thursday evening, July 2S. Its length on the wall is 6^ feet 

 nearly, and its breadth about two feet. It resembles the effect 

 produced by passing the shock of a battery through bits of gold 

 leaf pressed between two cards. At the same time, the electric fluid, 

 or stroke of lightning, dispersed -40 or 50 feet of iron bell-wire in 

 the lower rooms, and did considerable injury to the house and 

 furniture." N 



XII. Saccharomeler. 



The same gentleman has proposed the following query : — 

 " The saccharometer i^- an instrument used in common breweries 

 to ascertain the strength of infusions of malt, by their specific gra- 



