156 Progress of Invention. 



same spirit to resist innovations with a steady and powerful 

 force. Besides, the lake-dwellings may have been favourite 

 abodes for a fishing and semi-aquatic population, long after 

 they ceased to be desirable on the score of defence. Possibly 

 a diminution in the quantity of fish easily procurable had more 

 to do with the abandonment of these villages than anything 

 else. When fish abound, and a family can secure a dinner by 

 the simple expedient of suspending a few hooks and strings in 

 the water, the temptation to live close to, or on the water, 

 must be very strong. 



Many interesting questions concerning the lake- dwellers 

 remain to be worked out, but enough is known to warrant the 

 belief that in certain stages of human progress — not neces- 

 sarily coincident in point of actual time — the same mode of 

 living has been adopted by different races in various coun- 

 tries. The crannoge of Ireland bears some resemblance to 

 the pile-dwellings of Switzerland, and our own fen districts 

 will most likely show that we had our population of lake- 

 dwellers, when much of the land, now artificially drained and 

 dried, was permanently submerged. 



PROGKESS OF INVENTION. 



Photography with Dry Plates. — Photographers have never 

 ceased to look for a process by means of which dry instead of wet 

 plates might be used. Many such processes have been proposed ; 

 but though some of them have answered tolerably well, the greater 

 length of time required for exposure, and generally a want of 

 delicate graduation, and therefore of truth, in the tints and shadows 

 obtained, has prevented any of them from being generally adopted. 

 A want of complete success is the more unfortunate as the neces- 

 sity for using a wet plate involves a very large amount of trouble 

 and annoyance ; especially when mountainous and other places ac- 

 cessible with difficulty, are to be visited. This inconvenience which 

 has so long been felt, is now overcome ; at least so far as perhaps it 

 is possible to overcome it ; since a wet must ever be superior to a 

 dry plate in sensitiveness. The improved process, which is due to 

 Mr. W. England, consists in adding to eacli ounce of ordinary bromo- 

 iodized collodion, two grains of bromide of cadmium and two grains 

 and a-half of common resin, then shaking the bottle well and allowing 

 it to rest for a couple of hours. Alter this it may be used for coat- 

 ing the plate, which is sensitized by being placed for a few minutes 

 in a silver bath that contains forty grains to the ounce, and four 

 drops of nitric acid to the pint. The development is effected, after 

 running a little varnish round the edges of the plate <o prevent the 

 film from becoming loose, and (lightly washing, by ordinary ironsolu- 



