376 



C. B. Thwing — Photogi'aphic Method of 



magnet, and with a weak magnet the lines will not be suffi- 

 ciently distinct ; especially since it is necessary to employ a 

 considerable quantity of the iron filings in order to make a 



brilliant negative. 



Fig. 2. End of Bar Magnet. 



Fig. 6 was made on" a 5 by 8 plate with a four inch horse- 

 shoe magnet. 



Fig. 3. Bar Magnet. 



In fig. 7, six similar eight inch square bar magnets were 

 employed, and placed with alternate poles toward the center. 

 This is the arrangement commonly employed in the fields of 

 an alternating dynamo ; and the figure gives a very good idea 

 of the lines of force in such field. 



