A. M, Mayer — A large Spring-dalaim Electrometer. 513 



tions, but a few tests, made ou two small crystals by the usual 

 analytical methods, indicate that alumina is probably present, 

 while, from its association with herderite and bertrandite, 

 beryllium may be expected. AW have, therefore, undoubtedly a 

 new species, a phosphate (probably of beryllium and aluminum) 

 containing fluorine, and one which promises to be of unusual 

 interest. As it seems best to designate the mineral by a dis- 

 tinctive name we propose for it the name Hamlinite, in honor 

 of Dr. A. C. Hamlin of Bangor, Me., whose life-long interest 

 in the development of the mineral resources of his state, and 

 particularly of Oxford County (where this new mineral occurs), 

 has tended to make that region famous as affording some of 

 the most beautiful and highly interesting minerals known to 

 science. 



It is to be hoped that the mineral developments now going 

 on in Oxford County will bring to light an abundant supply of 

 this mineral, or enough, at least, to enable us to determine its 

 chemical composition. 



April 23d, 1890. 



Art. LYIII. — On a large spring-balance Electrometer for 

 measuring (Ijefore an audience) specific inductive capacities 

 <! nd potentials; by Alfred M. Mayer. 



This apparatus was devised by me for showing to my 

 classes the general phenomena of induction through various 

 dielectrics, and for making approximate measures of their 

 specific inductive capacities. These phenomena and measure- 

 ments are rarely shown to students, and when their exhibition' 

 is attempted the actions on the apparatus used are generally 

 too minute to be seen by a class, and hence the measures 

 deduced from these actions are unsatisfactory. 



The apparatus here described has done excellent service dur- 

 ing live courses of lectures. Its chief characteristic is that it 

 shows directly, and not inferentially, that different dielectrics 

 transmit the force of electricity in different degrees. 



The engraving gives a general view of the apparatus. A 

 helical spring, made of brass wire of *012 in. diameter and with 

 800 turns, is supported by a bracket formed of rods of glass. 

 These rods were dried by heating in a gas-flame and while hot 

 were coated with parafin. To the lower end of the spring is 

 suspended a disc of thin mica 16£ cms. in diameter, silvered 

 on its upper and lower surfaces in a silvering solution. This 

 disc, which was nearly flat, was made rigid and as nearly flat as 

 possible, by cementing (under pressure) to its upper surface 



