318 Intelligence and Miscellaneous Articles. 
determined in the preceding experiments, and which the writer had 
also the honour of submitting to the Society last session, is repre- 
sented in fig. 3. It is a very convenient modification of Gaugain’s 
instrument, described in the Annales de Chimie, vol. xli. 1854. The 
circular frame A, containing a variety of coils of different lengths 
and sizes of covered wire, is 9°6 inches in external diameter ; so that 
when the instrument is in use, the divided circle must be drawn out 
till its centre is 2°4 inches in front of the coil or coils through 
which the current is to be sent. To facilitate this operation, the 
horizontal bar D, upon which the disk slides, has the proper distances 
for each coil marked upon it, and these are successively exposed to 
view at the back of the instrument, in proportion as the disk is drawn 
smoothly forward by means of the handle C. The needle is only 
one inch in length, but carries parallel to itself a fine filament of 
glass for an index*; it is suspended by a silk fibre, and is raised so 
as to hang freely within its glass shade by turning the pin E. The 
ends of the coils are carried down through the hollow pillar B, and 
by connecting the electrodes of the battery with the proper terminals, 
the current can be sent through one or more of the coils. It canbe 
sent through one convolution of No. 16, through 203 convolutions 
of No. 34, or any other of the intermediate lengths and sizes of wire; 
and in this way the resistance and the force exerted by the current 
upon the needle can be very exactly adapted to the character of the 
battery, or other rheomotor employed.—From the Proceedings of the 
Glasgow Philosophical Society for January 16, 1861. 
ON THE PRESENCE OF ARSENIC AND ANTIMONY IN THE SOURCES 
AND BEDS OF STREAMS AND RIVERS. BY DUGALD CAMPBELL, 
ANALYTICAL CHEMIST TO THE HOSPITAL FOR CONSUMPTION, 
BROMPTON. 
To the Editors of the Philosophical Magazine and Journal. 
GENTLEMEN, 
Since my communication upon the above subject, published in 
the Philosophical Magazine of October last, I have repeated my 
experiments upon several of the sands I then reported upon, and 
with the like results which I then gave. I have also made experi- 
ments upon other specimens since obtained, and in all I have hitherto 
examined I have found arsenic, and generally, if not always, accom- 
panied with antimony. The process followed was the same as I 
formerly described, only I invariably used hydrochloric acid without 
the slightest trace of arsenic in it, as some doubts had been cast 
upon my former results, in a notice of my paper in the ‘ Chemical 
* The thickness of the index is grossly exaggerated in the figure; it 
ought to be as fine as a hair, and short in one arm. 
