PHILOSOPHICAL SOCIETY OF WASHINGTON. 47 



From these results it would appear that the aurora acts induct- 

 ively in the same way as a discharge of electricity acts. 



Mr. Theo Gill made a communication 



0J\ A TUNNY NEW TO THE AMERICAN COAST. 



22d Meeting. March 9, 1872. 



The President in the Chair. 



Mr. J. J. Woodward made a communication 



ON THE USE OF MONOCHROMATIC SUNLIGHT AS AN AID TO HIGH 

 POWER DEFINITION. 



{This paper is published in full in the American Naturalist, 1872, August, 

 vol. vi. p. 354.) 



(abstract.) 



In this paper Mr. Woodward recounted the various attempts 

 hitherto made to employ monochromatic sunlight for the illumi- 

 nation of the higher powers of the microscope, and claimed that 

 sunlight passed through a solution of the ammoniorsulphate of 

 copper, as first recotrmiended by Prof. J. W. Draper for photo- 

 graphic purposes, affords especial advantages for the definition 

 of difficult lined tests, such as Amphiplema pellucida, and the 

 Noberts plate. Several convenient methods of applying this 

 mode of illumination to microscopicaj objects were given in detail. 



Mr. J. E. HiLGARD made some remarks 



ON THE AURORA OF FEBRUARY 4tH. 



He said that since the last meeting of the Society accounts 

 had been received of the aurora borealis of February 4th having 

 been observed not only throughout Europe, but also in Egypt 

 and India. He had previously mentioned the account he had 

 received of its appearance in Texas, and had now to add that*it 

 had likewise been seen in California. It appeared thus to have 

 extended successively over at least two-thirds of the northern 

 hemisphere. It would be of great interest now to collect infor- 

 mation from vessels at sea between Europe and America, in order 

 to learn whether the phenomenon had been continuous. 



