294 New Self-Registerung Electrometer. 
This gentleman mentions that he has not extended his 
researches sufficiently to form a definite opinion as to the 
action of the three systems to which he refers, when the 
water is highly charged with carbonate of lime. Had he 
done so he would have found that in this particular case, 
silicated carbon would have had the advantage of Spencer's 
magnetic carbide and pure animal charcoal, on account of the 
presence of the pure silica. However, to reduce hardness 
of water, I would not entirely rely upon my favourite 
material, but get the assistance of other agents. Indeed, as 
I have stated before, an universal filtering medium does not 
in my Opinion exist. 
A competent person will not have much difficulty in 
devising means for an efficient purification of water, and a 
judicial arrangement will even overcome brackishness to a 
considerable extent. J have never had much trouble in 
reducing Thames water impurities to about half a grain of 
organic matter per gallon with a low degree of hardness. 
Messrs. Danks and Co., of Bourke-street will, in a few 
days, have a model apparatus which has been purposely 
constructed to suit the Melbourne water supply. It will 
entirely remove lead and reduce the organic matter to a 
minimum, without causing flatness. It can easily be attached 
to the supply-pipes without interfering with the existing 
arrangements, having also a simple and effective arrangement 
for the cleansing. : 
Another apparatus of a portable form will be particularly 
suitable for country use, at stations, farms, &c. 
ArT. XXV.—On a New Selj-Registering Electrometer ; or, 
Electrograph. By R. L. J. Evtery, Esq., President. 
[Read 9th December, 1867.] 
I have lately erected an instrument at the Observatory for 
obtaining a continuous record of the amount and variations 
of atmospheric electricity, the construction of which I 
believe is in some respects new ; Ihave therefore thought it 
worth while to lay a description of it before the Society. 
I must premise however that the maim principles of this 
electrometer are not new, but. were devised and applied by 
Sir W. Thomson, of Glasgow, some years ago, and he 
