NATIONAL GEOGRAFHIC SOCIETY'S ECLIPSE EXPEDITION 323 



character of most of these justify iis in ch\ssif3'ino; them as optical 

 illusions. To this class probabl}' belongs the seeming coming on of 

 the darkness l)y a series of waves. A chxss of phenomena seen so fre- 

 quentl}^ as to sliow that, whether purely optical or not, they follow a 

 law, and are due to some definable cause, are known as shadow bands. 

 An attempt was made to observe these on the plan outlined by the 

 Secretary of the Smithsonian Institution. While the observations, 

 through ail unfortunate neglect to make preparations in advivnce, 

 wei'e not carried out in all the detail recommended in the plan, re- 

 sults were obtained which may not be devoid of interest. 



'J'wo parties took part in the observation. One, a large one. oli- 

 served on the upper deck of the steamer as she lay at the navy yard 

 pier, the other on the })ier itself. Both made their observations on 

 several white sheets spread out on the deck or ground, the sliades on 

 which the\' carefully watched. 



From the steamer Mr Klbert B. Hamlin reported : '" Bands ]H)inted 

 northeast and southwest. The}^ vibrated at right angles to the way 

 they })ointed ; this l)efore totalit\'. Tlie}^ came on from the north- 

 cast. After totality they were less pronounced ; came on from south- 

 west and i)ointed noilhwest and southeast. They moved slowly and 

 were about two inches wide."' Some of the party laid down sticks to 

 show the direction of the bands, and inquiry was made by other 

 meml)ers as to the direction they noted. Although in most cases the 

 direction assigned agreed witli that of Mr Hamlin, one ol)server. at 

 least, saw the bands as lying northwest and southeast, while the tliree 

 ^ sticks ranged over more than 45 degrees. 



On the wliarf observations were made b}' Mr Claude Bennett and 

 several others. As Mr Bennett's observations were sent to the Smith- 

 sonian Institution for discussion and comparison, they neetl not l)e 

 given in full here. Thej' may be exi)ected to api)ear, with a nunil)cr 

 of (others, elsewhere. From verbal statements made on the spot by 

 Mr Bennett and two other observers, it would seem that tlxTc was no 

 agreement as to tiie natui'e of tlie plienoniena. Two obscrNcrs as- 

 signed a motion in opposite dii'ections ; tlie third saw no wcll-tldincd 

 motion and no distinct bands, but only an irregular tlickering. 



Some general remarks on the nature and c.-uise of these i>henoinena 

 sugixested by the preceding observations, may not lie oiu of place. 



Two possil)l(' hypoth(;ses are to be tested : (a) 'I'hat the variations 

 of light and slnule ai-e physi(;al i-ealities, and (7;) that they an' puicly 

 oi»tic:il. It is known that when an eye is suddenly nanovctl from 



