668 



SCIENCE. 



[N. S. Vol. XI. No. 278. 



to another. In this way the apparent brilliancy 

 of the sun can be varied at will, which would 

 increase the chances of detecting the flickering 

 if it existed. The location of the flickering is 

 to be carefully noted, that is, whether it is of a 

 portion, or the whole of the crescent, or whether 

 it is in the air close to the edge of the sun's 

 limb. The disc can be rotated by hand by 

 means of a whirling table, to be found in every 

 physical laboratory. This simple arrangement 

 will, I think, be found more satisfactory than 

 a more complicated rotator, as the speed is 

 more immediately under one's control. 



I am planning to use such an arrangement 

 myself, and hope that some of the other eclipse 

 parties can arrange for the simple experiment 

 also. The speed and width of the bands could 

 also be determined by means of the stroboscope. 

 If we receive the bands on a white cloth on 

 which a scale is marked, and view them through 

 the revolving disc, by carefully adjusting the 

 speed of rotation, it is obvious that the bands 

 can be made to appear stationary. Their width 

 can then be accurately determined by counting 

 the number in a given distance, and the speed 

 with which they move calculated, if the speed 

 of the disc at the moment is recorded. In 

 this way any change in width could be meas- 

 ured. 



While these observations can only be made 

 by persons who have had some training in work 

 of this nature, valuable data may be secured by 

 any who are fortunate enough to live within the 

 eclipse belt. I desire to secure, if possible, a 

 complete record of the appearance of the bands 

 over the entire country, together with state- 

 ments regarding the direction of the wind, con- 

 dition of the air, etc. The bands can be best 

 observed by spreading a sheet or other large 

 white cloth on the ground. As soon as the 

 moving shadows appear, which will probably 

 be about a minute before totality, lay a lath 

 on the sheet parallel to the shadows, with as 

 great accuracy as possible. Then try to esti- 

 mate the width of the bands, and the velocity 

 with which they are moving, also the direction 

 in which they are going, that is whether from 

 > east to west or west to east. The width of the 

 bands can be best determined, I imagine ( I 

 have never seen them ), by estimating the width 



of a group, say five or six, or as wide a bunch 

 as the eye can grasp and follow with certainty 

 as to the number of dark bands in it. A scale 

 for reference, preferably a white board with feet 

 and half-feet marked with strong black lines, 

 will be of assistance. It should be laid perpen- 

 dicular to the shadows, that is at right angles to 

 the lath. The speed can be estimated by trying 

 to keep up with the moving shadows, and may 

 be recorded as slow walk, fast walk, slow run, 

 etc. Those who are accustomed to counting 

 quarter seconds, can probably make a fair esti- 

 mate of the speed by noting the time of transit 

 of a band across the sheet. The shadows will 

 disappear at the moment of totality, but will 

 reappear again as soon as the sun's edge emerges 

 from behind the moon. A second lath should 

 be laid on the sheet, parallel to the bands un- 

 less their direction is the same, and the same 

 observations repeated, noting whether the direc- 

 tion of motion is reversed. After the eclipse is 

 over, determine the direction of the two laths 

 as accurately as possible with the compass, and 

 measure the angle between them. Note the di- 

 rection of the wind before and after the eclipse, 

 and record the general atmospheric condi- 

 tions. 



Tabulate the data as follows : * 



Before Totality. 



1. Direction of the bands. 



2. Width of bands. ( Give all data, that is, num- 

 ber of dark bands in given width of the system.) 



3. Estimated speed. State how estimated. 



4. Direction of motion. Whether from east to west, 

 or west to east. 



5. General appearance. Whether sharp or hazy, 

 vehether contrast between light and shadow is con- 

 siderable. If possible estimate relative intensity of 

 illumination in dark and light areas. 



6. Direction of wind. Temperature and general 

 atmospheric conditions. 



After Totality. 

 Repetition of the above. 

 Actual angle between the laths. 

 General remarks, and location of point of observa- 

 tion. 



Reports should be sent to Professor R. W. 

 Wood, Physical Laboratory of the University of 

 Wisconsin, Madison, Wis. 



R. W. Wood. 



