Makch 24, 1S99.] 



SCIENCE. 



457 



FTEOELECTRICITY AND PIEZOELECTRICITY. 



W. VoiGT {Wiedemann's Annalen, No. 13, 

 189S) shows that the electriflcatiou of certain 

 crystals by heating (pyroelectricity) and the 

 electrification by deformation (piezoelectricity) 

 are in general one and the same phenomenon, 

 and that it is only in such a crystal as tourma- 

 lin, which has a single axis distinguished from 

 all other axes by characteristic physical proper- 

 ties, that pyroelectricity is not due wholly to the 

 deformation accompanying a rise of temperature. 

 Professor Voigt also points out that a plate of 

 tourmalin can be used to generate accurately 

 known electric charges by subjecting it to 

 measured compression, and he gives the results 

 of a determination of an electrostatic capacity 

 based upon the known charge generated by a 

 tourmalin plate and the known e. m. f. of a 

 standard cell. W. S. F. 



THE ROTARY CONVERTER. 



In two short articles in the Electrical World, 

 for December 17th and 24th, Mr. C. P. Stein- 

 m^etz gives a quite complete discussion of the 

 theory and action of the rotary converter, a 

 machine used to convert alternating current into 

 direct current, mainly in connection with long 

 distance transmission. Mr. Steinmetz's papers 

 are, almost without exception, very difficult to 

 read for the reason, chiefly, that he always 

 gives a great deal of precise information about 

 difficult subjects not generally understood. The 

 present paper cannot, of course, be abstracted, 

 but it is mentioned for the reason that Mr. Stein- 

 metz deserves to be more generally known as 

 one of the foremost electricians of our time ; that 

 he is a scientific electrician is a matter of course. 



W. S. F. 



THE TELESCOPE-MIRROR-SCALE METHOD.* 



Professor S. W. Holman has given in the 

 Tecluiology Quarterly, for September, 1898, a 

 most complete and usable discussion of the tele- 

 scope-mirror-scale method for measuring angu- 

 lar deflections. Almost at the very beginning 

 of the paper a list of the fourteen instrumental 

 errors is given, together with directions for 

 making the adjustments which are necessary 



*Published separately by John Wiley & Sons, New 

 York. Price, 75 cents. 



to reduce each error to a prescribed value. 

 Following this is a general discussion of each 

 error of adjustment and a derivation of the 

 error in angle due to each. Most physicists 

 have, of course, looked into the detailed theory 

 of the telescope-mirror-scale method in spite of 

 the fact that the literature on the subject is not 

 generally accessible, but the habitual use of the 

 method for rough measurements makes one 

 lose sight of a dozen or more of the adjustments 

 and precautions which are necessary in accurate 

 work, and, therefore, almost every physicist 

 will find this pamphlet of Professor Holman's 

 a useful reminder when the need arises to use 

 the method with all the precision it is capa- 

 ble of. W. S. F. 



NOTES ON INORGANIC CSEMISTBY. 

 Some time ago a committee was appointed by 

 the German Chemical Society to formulate an 

 atomic-weight table which should serve as a 

 basis for practical use in analytical calculations. 

 This committee consisted of Professors Landolt, 

 Ostwald and Seubert, and has recently brought 

 in a report which has been widely published. 

 With three exceptions, the decimals in the 

 atomic weights are given only as far as the last 

 figure is practically correct. The weights as 

 far as given agree in general with those pub- 

 lished by Professor F. W. Clarke. The most 

 interesting point in connection with the table is 

 that the basis used is the atomic weight of 

 oxygen ^= 16. It is now a number of years 

 since Dr. F. P. Venable and others in this 

 country and abroad uttered strong protests 

 against the use of hydrogen = 1 as a standard, 

 especially since the atomic weights with few 

 exceptions are determined with reference to 

 oxygen, and at that time the ratio between 

 hydrogen and oxygen was uncertain. Now 

 that this ratio has been, thanks to Professor 

 Morley, rendered almost certain to three decimal 

 places, it is still unnecessary and unscientific to 

 bring in even this little uncertainty, which in 

 the elements of high atomic weight amounts to 

 quite an appreciable quantity. Professor Seu- 

 bert has been one of the strongest advocates of 

 the basis H ^ 1, and it is noteworthy that he 

 has agreed to the committee report. In the 

 report Seubert says that, while H = 1 is in 



