95 
A few determinations were also made with the grain of both block and plate 
horizontal, the other circumstances, curvature and height, being the same as in 
the above table. 
These results are given as they be of interest but very little reliance can be 
placed upon them as they were somewhat hastily made and time did not permit 
of repetition. 
Material. Value of e. Duration of Contact. 
Witter ova sani SAI Buh eS Aerariag sia ake ole .0024 seconds. 
Ohennymeis of see he siepeas hs Pe eet eRe pet ph MS Pr 0014 ec 
Panduinia pl elev jes ate. ADO Ra Mee, ANTM icet Mtoe .0012 rt 
These seem to show in a more pronounced manner the connection between 
duration of contact and the coefficient of restitution, but for reasons above stated 
we hesitate to regard the law as established. 
It may be added, by way of a postscript of less serious content, that the length 
of time of contact of a base ball with a bat and the corresponding value of the 
coefficient of restitution, were determined by this method. These values are for 
the duration of contact ;+,; seconds, and for the coefficient of restitution %. 
VARIATIONS IN THE SPECTRUM OF THE OPEN AND CLOSED ELEcTRIC ARC. 
By ArtHur L. FoLry. 
[Abstract.] 
The image of a normal electric are appears to consist of three regions— 
a central violet portion, an outer yellow sheath or flame and an intermedi- 
ate sheath of blue. By means of a Rowland grating and a Brashear 
mounting, and a concave mirror to focus the image of the are upon the slit, 
a photographic study was made of the spectra of these regions under four 
conditions: (1) A vertical are and a vertical slit, (2) a vertical are blown 
out by a horseshoe magnet, (8) a horizontal arc and a vertical slit, (4) a 
horizontal are and a horizontal slit. 
The accompanying table gives the results of a study of the three re- 
gions of the arc with the slit vertical and through the center of each 
region. Two exposures were made in each position, three seconds and 
thirty seconds in the violet and blue regions, ten seconds and thirty sec- 
onds in the outer or yellow sheath. An exposure of three seconds in the 
latter brought out only ten lines. 
