progress could be compared to that of a great atmospheric wave, the pressure being more steady aod persistent on the one side (in this case the west) than on the other. Prof. H. A. Rowland exhibited a. tabular view of the different values which had been given to the ohm, and criticised that which bad received the sanction of the Paris electrical conferCDce as an average derived by giving equal weight to values obtained by admittedly unequal methods. By adding to the table of the Paris conference the results reached by the American committee in its investigations, and allowing each result its proper p]'0[x>rtion3l value, he had obtained a column of mercury of one square millimetre section and 10G.2 centime- tres high as a satisfactory average, which the American committee therefore recommends.
Perhaps the greatest public interest atlaciied to the two papers of Dr. Graham Bell, given on the last day of the session, one on the possi- bility, while at sea in a fog, of detecting by means of echoes the proximity of dangerous objects. Mr. Delia Torre and Mr. Bell had experimented by means of a gun and a receiv- ing-trumpet, and had obtaine<l echoes from passing vessels at a distance of from a quarter
- to a mile, according to their size.
The other showed the results of some experi- ments he had made on the audition of school- children of Washington. He exhibited an audiometer he had devised, in which two flat coils of insulated wire were so adjusted as to admit of separation on a graduated scale meas- uring the distance between their centres. An electrical cunent. produced by the rotation of n Siemens armature between the poles of a permanent magnet, is passed through one of the coils, and is rapidly interrupted by the rota- tion of a disk, a telephone being attached to the other. The intensity of the sound pro- duced being dependent upon the intensity of the current induced in the coil to which tbe telephone is attached, and this upon the dis- tance between the coils, a ready measurement of audition is obtained. The use of this instru- ment proved that ten per cent of the more than seven hundred pupils examined with the
��assislnnce of Mr. H. G. Rogers were hard of hearing (in their best ear), and sev' cent had very acute powers; the general range of audition being measured - on the scale by the separation of the disks to a distance of from fifty to eighty centimetres, while the total range was from twenty to ninety centimetres. It is known, on the oilier hand, that in some institutions for the deaf as many as fifleeu per cent are merely hard of hearing.
Dr. Ii a Remsen brought to the notice of the academy a case in which chemical action was affected by magnetic influence. Placing a test- tube containing nitric acid in the middle of a coil through which a current was made to pass, he found that the action of the acid on a strip of iron placed in it was sensibly lessened, by at least ten per cent, when compared with that of another strip of iron placed in similar circumstances excepting for the absence of the electric cuirent. Dr. Sterry Hunt proposed a classiflcation of the natural silicates which make up a large part of our earth's crust, di- viding them into three groups, accoi-diug to their bases, and distinguishing them as proto- silicales, persilicates, and protopersilicates. These divisions lie believed were more natural than those which divided them according to their sensible qualities, or otherwise, and indi- cated genetic distinctions.
On the biological side, the papers, while perhaps not so attractive to the public as those already mentioned, were of more than usual philosophic interest. Prof. E. D. Cope, in a communication on the pretertiary verlebratefl of Brazil, which were referred to the cretaceOQS, Jurassic, and upper paleozoic, and which con- tained many interesting types, pointed out also that a single pliocene fauna extended fh>m south of our borders to Patagonia, and that neither eocene nor miocene beds had been dis- covered in South America. In a more elab<K] rate paper on the phylogeny of the placeni mammalia, based largely on discoveries ii western parts of North America, he claimed) that while many details remain to be work* out, and though their didelphiau ancestors had;
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