46 A. G. Bell—Apparatus for determining the Position of a 
recent genus in which a similar structure still exists is Agassiza. 
n this genus, however, the posterior lateral petals are nor- 
mally developed, as in other Spatangoids; or perhaps we must 
consider this as the last trace in normal Spatangoids of the 
simple condition of the ambulacra, such as we still find it in 
the Pourtalesiz. It is specially eae to compare these 
genera first to the Ananchytide, then to the Toxasteride ; and 
finally to such recent genera as "Geniopatges, Homolampas, 
Argopatagus, and the like. ese comparisons lea to 
detect affinities in all possible directions, with ae, highly sein, 
loid ambulacra of the Spatangoids, with the simplest ambula- 
eral petals of the earliest Spatangoids, or with the embryonic 
ambulacra of the Pourtalesiz proper. 
Art. V.—Upon an Apparatus for determining without pain to 
the patient the Position of a Projectile of Lead or ner metal in 
the human body ; by ALEXANDER GRAHAM BELL. 
THE instrument I have the honor of presenting to the Acad- 
emy has for its object the determination of the exact place 
occupied by balls of lead, sc of peal, or metallic sub- 
stances of any kind en mbedded in in the body of a person wounded 
by fire-arms, and it may be oabsiystor as a form of the well- 
known Induction Balance of Professor Hughes 
This exploring instrument enables us to determine that posi- 
tion for the most part with very great exactness, and that si 
out any pain to the patient, which is not the case when we use 
metallic probes which require to be brought into direct sda 
with the projectile. 
The instrument is rea gaeee essentially (fig. 1) of a system 
of two parallel flat coils (A and B) partially superposed upon 
one another in such a manner that the edge of one is nearly 
*This instrument has originated ahah researches undertaken in the Volta 
Laboratory at Washington, on the occasion of the sad attempt upon the life of 
President Garficld. This note is ccanvalniee to a paper which I shall aagres 
y, givi giving a complete account of these researches. It was read befor 
renc. i 
t persons have been kind enough to give me the benefit of 
their suggestion ms pes advice, concerning the method of exploration for this object, 
that I can only mention here the names of a ew: 
Hite es, George M. Hopkins, pps Taintor, Thomas Gleeson, Dr. Chi- 
chester A. Bell, Charles E. Buell, Prof. Simon Newcomb, Prof. H. A. Rowland, 
M. Rogers, Prof. John Trow bridge, J. H. C. Wa tts, the director of the Western 
Union Telegraph Co. at Washington, and the e correspondent of the New York 
ribune at Washington. 
