146 THE SEVEN FOLLIES OF SCIENCE 



hereafter the ordinary methods of searching suspected 

 spies will have to be exchanged for one that is more 

 efficient. 



The most interesting application of microphotography, 

 of which we have any record, occurred during the Franco- 

 Prussian war in 1870-71. 



On September 21, 1870, the Germans so completely 

 surrounded the French capitol, that all communication by 



Fig. 21. 



roads, railways, and telegraphs, was cut off and the only 

 way of escape from the city was through the air. On 

 April 23, the first balloon left Paris, and in a short time 

 after that, a regular balloon post was established, letters 

 and packages being sent out at intervals of three to seven 

 days. In order to get news back to the city, carrier 

 pigeons were employed, and at first the letters were simply 

 written on very thin paper and enclosed in quills which 

 were fastened to the middle tail-feather of the bird, as 

 shown in the engraving, Fig. 21. It is, of course, need- 



