374 CARNEGIE INSTITUTION OF WASHINGTON. 



my return from Germany. A complete transcription of it, accompanied 

 by a paleographical introduction, is being prepared for publication. 



The latter part of 1914 will be taken up with revising and publishing 

 the letterpress to go with the collection of plates entitled "Scriptura 

 Beneventana. ' ' The collotype facsimiles have already been printed. In 

 the autumn I shall have the honor of delivering the Sandars lectures — 

 four in number— before the University of Cambridge, and seven lectures 

 on the history of Latin writing before the University of Oxford. 



PHYSICS. 



Barus, Carl, Brown University, Providence, Rhode Island. Study of diffusion 

 of gases through liquids and provision for applications of the elliptic inter- 

 ferometer. (For previous reports see Year Books Nos. 4, 5, 7-12.) 



In the early part of the year. Professor Barus continued his experi- 

 ments with the quadrant electrometer, made specially sensitive by 

 providing the needle with two light, symmetrically parallel plane 

 mirrors, about 5 centimeters apart. One of the component beams of 

 the displacement interferometer, impinging at an angle of about 45 

 degrees, passes from the first mirror to the second, thence to the distant 

 fixed mirror, from which it is normally reflected and returns in its path. 

 It should be possible, in a quiet laboratory, to measure voltages as 

 small as 10 micro-volts per vanishing interference ring, so that single 

 micro-volts could be reached by estimation. In the large number of 

 experiments made, the optical adjustment presented no serious diffi- 

 culty. It was found exceedingly troublesome, however, to adapt the 

 behavior of the electrical apparatus to the same degree of sensitiveness. 



Throughout the year the application of the displacement interfer- 

 ometer to the horizontal pendulum has been the chief subject of inves- 

 tigation. A number of methods were devised and tested in detail, 

 among which was the above method of two parallel mirrors, on a sym- 

 metrical pendulum beam, loaded on one side. With the mirrors a 

 meter or more apart, the sensitiveness is correspondingly increased. 

 It is simpler, however, to replace the two opaque mirrors of the inter- 

 ferometer by two identical concave mirrors, having their foci at the 

 grating. If the focal distances are large enough, say 1 meter or more, 

 the grating may then be rotated on its axis as far as the mirrors will 

 allow (several degrees), without seriously disturbing the interferences. 

 This is in excess of anything required by the horizontal pendulum. 

 If, then, the rotational defect is eliminated, the displacement of the end 

 of the horizontal pendulum may be measured as usual. The apparatus 

 with which the measurements were made was built for experimental 

 purposes and not for extreme refinements; but with the grating at 

 111 cm. from the nearly vertical axis of the pendulum, the horizontal 

 angle corresponding to a vanishing interference ring was 0.028". 

 Hence, for an inclination of the axis to the vertical of about 0.6°, the 



