PROCEEDINGS. 
541 
which their ends project, making good electrical contact with these blocks 
and thus with each other. This gridiron arrangement, the length of 
which is about six times its width, is then bent in the middle, so that 
one half lies above and parallel to the other, their planes being separated 
by about one inch. 
When a current is led into one end of one of the end blocks it divides 
nearly equally among the parallel rods and returns to the opposite end 
of the other, producing an approximately uniform magnetic field in the 
inclosed space, as well as in the space immediately above. A needle of 
proper dimensions may be placed in either of these positions and a large 
range of sensibility is the result. The instrument may be calibrated by 
any of the ordinary methods. 
338th Meeting. May 25, 1889. 
President Eastman in the chair. 
Thirty-fonr members present. 
The Chair announced the death of Mr. E. B. Lefavouk, a 
member of the Society. 
Mr. E. D. Preston read a paper on The Reduction of Pendu¬ 
lum Observations. 
Published in full in this volume, pp. 115-130. 
Mr. J. P. Iddings read a paper on The Crystallization of Igne¬ 
ous Rocks. 
Published in this volume, pp. 65-113. 
Mr. W. H. Dall made a communication on Some Forms of 
the Gill in Pelecypod Mollusca. 
The facts of this paper are incorporated in Mr. Dali’s report 
on The Gasteropoda and Scaphopoda: Bulletin Museum of 
Comparative Zoology, Cambridge, vol. 18, June, 1889. 
339th Meeting. October 12, 1889. 
President Eastman in the chair. 
Forty members present. 
The Chair announced the election to membership of Mr. 
Oliver Lanard Fassig. 
