M. I. Pupin — Electrical Oscillations, etc. 503 



Having the material deposited, adequate to furnishing a 

 supply of phosphoric acid, the process of change to the present 

 forms followed as a natural consequence, from the attendant 

 circumstances in due course of law. The guano beds after the 

 leaching out of their carbonates and other soluble materials, 

 became very compact, yet not entirely impervious to water. 

 It is probable that some waste of material by solution is con- 

 tinued in degree to the present day. 



Cavities are found in the most compact beds of the " hardest 

 rock." Small cavities in close contiguity became finally sepa- 

 rated by mere plates, and in this condition are called " lami- 

 nated-rock." 



By further disintegration such laminated rock is broken up 

 into fragments greater or less, and is then " plate-rock " — such 

 as is found mixed up with more finely comminuted material in 

 the deposits of Anthony and Sparr and Fair view clinging to 

 the walls of the pinnacles of Eocene limestone. 



Still further progress of the disintegrating process results in 

 the masses of "soft-phosphate" — the impurity of the final 

 material depending in part upon the amount of clay originally 

 contained in the immense deposits of the original rock, and 

 partly upon the amount of extraneous matter washed in. 



That the fragments of "plate-rock" should cling to the walls 

 of the pits is the natural result of drainage being more ener- 

 getic in the center of the hopper than at the sides; at the same 

 time the middle portions become dissolved or reduced more 

 quickly and more completely than the exterior. 



Art. LXI. — On Electrical Oscillations of Low Frequency 

 and their Resonance; by M. I. Pupiisr, Ph.D., Columbia 

 College. 



Part II. 



[Continued from page 429.] 



V. Electrical Resonance in mutually inductive circuits. 



a. The impressed Electromotive force is a simple harmonic. 

 — The primary circuit consists of a coil which is in series with 

 a condenser and an alternating current machine which gene- 

 rates the impressed e. m. f. E sin pt. The secondary circuit 

 consists of a coil joined in series to a condenser. The second- 

 ary coil consists of several parts, some or all of which are 

 under the inductive action of the primary circuit. The 



