Instantaneous Photography 

probably because the shutters giving shorter exposures than this are not met with every day. In the first column above, the distances of the object are expressed as multiples of the focal length; the distance in yards is easily reckoned out by multiplying by the focus of lens. Thus, an object is 200 times the focus of lens distant, and using anlens, then :
These distances must be estimated by measurement or guess work. This latter is by no means difficult to reach; thus the following table, compiled by the same writer, will be of assistance. We assume that the mean height of a man is 5 ft. 9 in. that of a horse 5 ft. 3 in., that when the height of the image of horse and a man appears on the groundglass as : 







Another table compiled by MM. Henry Hermagis and Rossignol is also convenient:  







* The exposure to be made at the moment of partial rest or least movement. t Object moving across the field of view.
406 
