THE BOOK OF THE LANTERN. 181 



S. Pichler, who designed various other ingenious contriv- 

 ances. He was very jealous about this astrometeoroscope, 

 and the onlj one made was at the Polytechnic Institution, 

 where it was carefully kept under lock and key, except 

 when in actual use. When the apparatus of the institution 

 came to the hammer, I remember that there was some 

 little excitement when the astrometeoroscope was put up 

 for sale. Opticians and others would have been glad to 

 get hold of it, so as to have multiplied it for sale. This led 

 to a brisk competition, ending with Mr. Pichler giving an 

 extravagant price for his own bantling. And in that way 

 the secret remains in the hands of a few only, and perhaps 

 it would be unkind to divulge it. But, at any rate, I 

 cannot do much harm by giving a general idea of the out- 

 ward appearance of the instrument and its capabilities. 



The astrometeoroscope consists of a narrow box thirteen 

 inches in length, and of such a width that at one end it 

 will fit the stage of the lantern. At this end it has the 

 usual three-inch disc opening, which is occupied by two 

 plates of metal which are scored across obliquely with slits 

 and which are superposed one. on the other, so that the 

 slits on each cross one another diagonally. Now it 

 is clear that the only places where light can pierce 

 these plates of metal so as to make itself evident on 

 the screen is in those places where the slits on the plates 

 intersect one another. The effect on the screen, therefore, 

 whilst the instrument is quiescent, is a series of dots of 

 light all over the screen, but at regular distances from one 

 another. By very ingenious mechanism the two plates are 

 caused to move to and fro in contrary directions, and the 



