Hidden and Penfield—HanditiUefrom Stonekam, Me, 511 



Finally the work of the present paper may be looked at from 

 quite a different point of view. Suppose for instance, 1 regard 

 the linear isometric proposed by Ramsay and 5Toung (1. c.) 

 an established fact. Then the chief result of the present 

 work, viz: that the exponential equation (2) if applied to the 



served changes of volume predicts a linear isometric through- 

 out an enormous range (A' pressure, affords favorable evidence 

 of the truth of the exponential equation in question. In 

 other words, it is probable that along any isothermal compres- 

 sibility increases inversely as pressure increased by a constant. 

 The interpretation of this constant cannot now be given. 



Since the above work was done, I have succeeded in con- 

 structing a screw compressor,* by aid of which 2000 atm. may 

 be hydrostatically applied with facility. I have also con- 

 structed gauges suitable for the accurate measurement of such 

 pressure. The general adjustment is of a kind that all nec- 

 essary electric insulation of different parts of the apparatus is 

 guaranteed, so that most of the measurements may be made 

 electrically. With these advantages I hope to subject the data 

 which the above pages have tentatively outlined, to a direct 

 and more searching test. 



Phys. Lab. U. S. G. S.. Washington, D. C. 



Art. LYII. — On Hamlinite, a new rhombohedral Mineral 

 front the Herderite locality at Stone/iam, Me. / by W. E. 

 Hidden and S. L. Pexfield. 



Shortly following the announcement of herderitet from 

 Stoneham, the mineral, which we are about to describe, was 

 detected by one of us occurring as minute rhombohedral crys- 

 tals attached to the herderite and margarodite and associated 

 with a mineral which was subsequently identified as the rare 

 beryllium silicate, bertrandite. As the crystals were observed 

 on only a single specimen and would not have weighed much 

 more than 0*01 gram, if they could have been successfully 

 detached from the matrix, it seemed imperative that more 

 material should be obtained before commencing any investiga- 

 tion. During the past five years, therefore, we have kept up 

 a diligent search for the crystals, examining carefully every 

 available herderite specimen ; we have also informed various 



* A description of this apparatus will be found in the Transactions of the 

 American Academy of the present year. I have now done much work with 

 ether, tracing the isometrics directly as far as 1850 atm. and something over 21f»°, 

 without however being able to reach a decision. May, 1 800. 



f This Journal. III. xxvii. pp. 7:5 and 135, L884. 



