346 Scientific Intelligence. 



vious analyses, the mineral analysts will be slow to give up the 

 convenient and tangible oxides and anhydrides. The present 

 method of calculating a mineral water analysis shows what actual 

 salts would make a similar water, while an analysis stated in the 

 ion form would be of little use, without recalculation, to physi- 

 cians or others who wished to know its character. h. l. w. 



3. Note on the telephonic measurement of electromotive force : 

 by C. Baeus. — According to de la Rue, Ferraris, Pellat and 

 others, currents as small as 10 -9 are still audible in the telephone. 

 One is therefore warranted in replacing the galvanometer in a 

 shunted circuit for the measurement of electromotive force (zero 

 method) by the telephone, seeing that the sensitiveness stated 

 would suffice for measurements much exceeding the constancy of 

 any galvanic cell. Devising a special key for the purpose, I made 

 this test; but I did not find the extreme sensitiveness stated. 

 Even in specially wound telephones of 6000 turns of wire, the 

 best result I could obtain was an audibility of lO -1 amperes, 

 under the following remarkable conditions : For increments of 

 current amounting to 3*1 X10 -7 on either side of zero the tele- 

 phone did not respond at all. On both margins of this silent 

 held, however, the response came in a way to make further incre- 

 ments of only 10 - ' 7 amperes quite distinguishable in loudness. 

 Here therefore is a true discontinuity, for the extent of the inter- 

 val of silence is at least 5 times the sensitiveness of the telephone 

 on and beyond the margins of this interval. In the great variety 

 of experiments made this result was the invariable feature, the 

 silent interval being in some cases even 10 or 20 times the mar- 

 ginal sensitiveness. 



I interpret this to mean that the diaphragm of a telephone 

 when in a state of rest initially resists deformation with a kind 

 of molecular quiescent friction; and that this inertness must 

 first be overcome by the actuating field before the diaphragm 

 responds nicely to fine gradations of stress. 



4. A Laboratory Manual of Physics and applied Electricity • 

 arranged and edited by Edward L. Nichols. Vol. I, 294 pp. 

 Vol. II, 444 pp. (New York, Macmillan & Co., 1894.)— The recent 

 development or Laboratory practice and the important place 

 now assigned to experimental physics in the college curriculum 

 causes us to welcome this present work. 



The manual is divided into two volumes, each of which con- 

 stitutes a complete and separate work in itself covering its par- 

 ticular field. 



Volume I is entitled a Junior Course in General Physics and 

 is the work of E. Merritt and F. G. Rogers. The field of me- 

 chanics, heat, light, electricity and magnetism is covered by well 

 selected experiments arranged in groups according to the subject 

 matter. This volume, intended as it is for first year students, 

 admits of little originality as to material and the sole value of 

 such a work depends upon the method of presentation and in 

 this the work merits commendation ; it is free from dead wood, 



