160 Intelligence and Miscellaneous Articles. 
derates. If the above proportions of oxygen may be expressed by 
the numbers 9:5:2:12:9, Beudantite is 
4Fe? 03 + 2PbO +3803 + PO®+9HO, 
and is therefore a very peculiar double compound, which might be 
written 9PbhO SO3 +Fe? 03 SO3 + (Fe? 03)3 PO’ +. 9HO, 
er 2(PbO)3 POs + (Fe? 03)’ PO? + 9Fe? 03 SO} +27HO. 
—Poggendorff’s Annalen, vol. c. p. 579. 
THE IMPROVED INDUCTION COIL: 
To the Editors of the Philosophical Magazine and Journal. 
128 Sloane Street, 
GENTLEMEN, July 4, 1857. 
Mr. Hearder, in his last letter to you, has again asserted that the 
induction coil contrived by me is perfectly similar to the instrument 
invented by himself. This is the fourth time he has made this asser- 
tion; and as it is always accompanied by his claim to priority, it 
makes it appear that I had really copied his machine, or adopted his 
ideas on the subject. 
As my coil has, for protection, been enclosed by a box which has 
not been opened in Mr. Hearder’s presence, he may not be aware of 
the dissimilarity of our instruments. First, Mr. Hearder uses a 
gutta-percha bobbin for his secondary helix, and winds the wire to 
be placed thereon until it is close to the cheeks of the bobbin. ‘This 
method was adopted by me at first, but I found that the sparks passed 
from the upper layer of wire to the lower one, ‘To prevent this I 
constructed my present coil without a bobbin, and wound my wire so 
that each layer was shorter than the one beneath ; the intervals thus 
left were filled by the gutta-percha tissue with which I insulated the 
layers of wire. ‘The coil thus assumed the form of a cylinder having 
rounded ends, and the space thus gained was sufficient to prevent 
the discharge taking place between the inner and outer layers of | 
wire. By adopting this arrangement, Mr. Ladd of Chancery Lane 
has constructed an instrument which gives sparks 43 inches long in 
air of the natural pressure. 
My iron core also differs from Mr. Hearder’s, and is formed of 
very fine parallel wires, each wire being magnetically and electrically 
insulated from the others. I formed it thus because such a mass 
cun be magnetized and demagnetized with greater celerity than any 
other arrangement, and allows me to break contact with the battery 
from 50 to 2000 timesa second. ‘This rapidity of action was noticed 
by Mr. Hearder at the London Institution as being peculiar; and it 
also allows me to obtain a beautiful arc of flame between the second- 
ary terminals, instead of sparks following each other slowly. 
I could name other peculiarities, such as using a great number of 
coatings of thin gutta-percha instead of fewer layers of thick tissue, 
&c., but I think the differences which I have pointed out will be sufii- 
cient to show that I have not copied Mr. Hearder’s induction coils. 
Trusting you will excuse me for again troubling you, I remain, 
Yours very obediently, 
C. A, Bentuey. 
