Chemistry and Physics. 173 



forth an absorption region at a desired place without influencing 

 the remaining spectral region. If another coloring substance 

 could be found which added to the thorium mantel could blacken 

 not only the short waves of the visible spectrum but also the yel- 

 low and red without disturbing greatly the ultra-red, the light 

 workino- of the burner would be increased three times. — Ann. cler 

 Physik, No. 14, 1905, pp. 725-738. J. t. 



8. Afterglow produced by Lightning Discharges. — E. Touchet 

 (Compt. Rend., cxl, p. 1031, 1905) accounts for this by the sup- 

 position of an after-heating of the air. K. E. F. Schmidt (Elektro- 

 techn. Zeitschrift, xxvi, p. 903, 1905) believes that it is a phos- 

 phorescent effect. B. Walter gives his reasons for supposing 

 that it is due to an after-discharge of electricity along the first 

 path of the original discharge. — Ann. def Physik, No. 14, 1905, 

 pp. 863-866. J. t. 



9. Specific Heat of Superheated Steam. — Regnault in his 

 investigation on this subject used a water calorimeter at the tem- 

 perature of the room. This method had the disadvantage that 

 the steam condensed in the calorimeter. To avoid the resulting 

 errors Regnault let steam at 128° and afterwards at 217° stream 

 through the apparatus. L. Rubens and F. Hehning use paraffin 

 oil instead of water above 1 00° and thus avoid the condensation 

 of the steam, and proceed as with non-condensing gases. 



They obtain the result C = 0,4410 (1 -f 0,00014^(9). — Ann. der 



Physik, No. 14, 1905, pp. 739-756. j. t. 



10. Use of the Microphone Contact for Telegraphic Pelays, 

 and for Detection of Weak Currents. — It has occurred to many 

 inventors that a relay might result from simply placing a micro- 

 phone contact against the vibrating disc of a telephone. It was 

 soon realized that the excursions of such a disc were too small to 

 actuate efficiently such a microphonic contact ; moreover the 

 pressure of the contact on the disc interfered with the vibration 

 of such a disc. Chk. Jensen and H. Sieveking have taken up 

 the general subject of microphonic contacts with the view of 

 using them in some form of telephonic relay. In order to shun 

 disturbing vibrations the microphonic contact was placed on a 

 Julius suspension consisting of a heavy board or table hung from 

 the ceiling with the usual arrangement of supporting wires. 

 They found this suspension very useful. No mention, however, 

 is made of the singing of microphonic contacts ; a trouble which 

 is very difficult to overcome in the practical use of any micro- 

 phonic contact. Possibly the currents employed by these investi- 

 gators were too feeble to cause this singing. The paper contains 

 a great many measurements - of microphonic resistances and con- 

 cludes with the following questions which were suggested by the 

 investigation. 



(1) What sensitiveness must one desire in order to obtain a 

 practical working telegraphic relay ? 



(2) In avoiding shaking or other disturbances within what 

 limits is it safe to work without the necessity of too delicate 

 adjustments? 



