CONTINUOUS IMAGES OF LIGHTNING. 679 



RUSSIAN EXPEDITION TO THE BAY OF OBI. 



Colonel Veninkoff has written some details on the Russian Expedition sent 

 in the spring of 1881, under the direction of Colonel Moisseef, to the Bay of Obi. 



The explorers have followed the eastern shore of the Bay between the 67 ° 

 and 72° latitude, and by their astronomical observations have demonstrated the 

 fact that on our maps we must move the coast from 20 to 25 kilometers more to 

 the west. On the other hand the Bay of Obi being reduced in width, the penin- 

 sula between the Obi and the Taze is largely increased in width. 



At the mouth of the Lena a meteorological and magnetic station is to be es- 

 tablished. As we have before stated, the expedition charged with this work has 

 just started from St. Petersburg. The Russian Geographical Society which has 

 taken the initiative in concert with all other scientific institutions that are instruct- 

 ed with the realization of the project of Comte Wilezek. 



The observer selected for this station is a young man, Mr. Yurgens; who to 

 reach his destination, will have to travel 3,000 kilometers in a sleigh, then 3,000 

 kilometers in a bark or in canoes. 



He is to return at the end of one year. We will thus have an uninterrupted 

 set of observations regularly taken and maintained in a circumpolar station, 

 which is something of which there is almost a total want. 



OPTICS. 



"CONTINUOUS IMAGES OF LIGHTNING." 



BY PROFESSOR FRANCIS E. NIPHER. 



The phenomena described by Mr. Blair in the February number of the 

 Review is one which can be reproduced at any time by looking at any bright 

 object, like a gas flame or even a candle. The explanation is correctly referred 

 by the editor to a residual effect upon the retina. 



If a gas flame is observed by fixing the eye steadily for a few seconds upon 

 some point near the flame, and if the eye is then closed or turned quickly to a 

 darker part of the room, an after image of the flame will be observed. This 

 eff'ect lasts but a short time and requires careful observation in order to see it un- 

 less the object viewed be bright. Nevertheless, the part of the retina upon which 

 the image of the flame was formed is still in a difi'erent condition from the rest of 

 the retina, and this may be seen by turning toward the flame again, so that the 

 light will again enter the eye, at the same time opening and closing the eyes 

 rapidly. The after image will again come out in a most vivid manner, and can be 

 si.en for several minutes. This reproduces the same conditions under which Mr. 



