384 CARNEGIE INSTITUTION OF WASHINGTON. 



A very satisfactory experimental equipment tries out the effect (if any) of 

 an electric current on rays of light. These pass in parallel with the current 

 through the same long channel, both in case of an exhausted tube and of an 

 electrolytic trough. Such an effect was hardly to be expected and none was 

 found. In the sequel some useful improvements are added to the self-adjust- 

 ing interferometer. 



An endeavor is made to ascertain to what degree the constant of gravita- 

 tion may be found in a self-contained apparatus under ordinary laboratory 

 conditions, and it contains two groups of measurements. The first, made in 

 a moderate vacuum oi a few milhmeters and with a relatively thick quartz 

 fiber, gave a value trustworthy within 1 per cent. Thereafter a much thinner 

 fiber was tested, giving excursions 5 to 10 times larger, the needle swinging 

 in partial vacua. The mean elongations of the needle at night seem to 

 be trustworthy; but the long period of the needle could not now be found 

 with anything like adequate accuracy. So dependent is this period on the 

 thermal environment that early morning and afternoon observations may 

 vary from 600 to 800 seconds, the individual data themselves being quite 

 accurate. A storm passing over the laboratory dropped the period from 750 

 to 626 sec, after which it rose again to 712 sec. Of course it would be possible 

 to determine the modulus of the fiber by a separate small body; but this would 

 be at variance with the plan of the experiments. The work will be resumed 

 this summer under the highest attainable exhaustions, as the experiments 

 show this to be indispensable. 



Hayford, John F., Northwestern University, Evanston, Illinois. Investi- 

 gation of the laws of evaporation and stream-flow. (For previous reports see 

 Year Books Nos. 12-16, 19, 20.) 



One year ago the evaluation of the effects of winds and of barometric 

 pressures in disturbing the elevation of the water surface at Buffalo and Cleve- 

 land on Lake Erie, and at Milwaukee, Mackinaw, and Harbor Beach on Lake 

 Michigan-Huron, had been completed. It was then decided that the next 

 step should be the determination of laws of evaporation from the surface 

 of the lakes and the incidental determination, so far as possible, of the laws 

 controlling stream-flow into Lake Michigan-Huron and into Lake Superior. 



These two lakes were chosen, on the basis of the extensive prehminary 

 investigations already made, as being the ones for which the greater accuracy 

 would be secured in the determination of evaporation and stream-flow from 

 a given amount of work. On each of these lakes the elevation of the mean 

 surface of the whole lake, and therefore the total water-content of the lake, 

 may be determined for each day with a much higher degree of accuracy than 

 is possible for Lake Erie or Lake Ontario. It now appears that the probable 

 error of the computed change of elevation in one day of the mean water-sur- 

 face of either Lake Michigan-Huron on Lake Superior is less than ±0.02 

 foot. That is, the change of elevation of the mean water-surface, from any 

 day to the next, may be computed so accurately from the observed meteoro- 

 logical facts around the lake — humidities, temperatures, rain-fall — that the 

 computed value will be within 0.02 foot of the truth in more than half of the 

 cases. 



