PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 451 



upon the bolt is renewed. In another variety of tliis class the tumblers 

 move partly in one direction and partly in the other. 



The senses that can be made available in lock-picking are seeing, hear- 

 ing and feeling, and all the devices which have been invented for increas- 

 ing the security of locks have been intended to baffle these senses. All 

 locks constructed up to a certain period can be opened by feeling the pres- 

 sure imparted to the obstructions by the effort to withdraw the bolt, or by 

 tracing the impression left by the key along the bellies of the tumblers. 

 But these operations were prevented by constructing locks without key- 

 holes; the obstructions being adjusted by means of a dial and index on the 

 outside, or by having the keyhole entirely closed during the movement of 

 the bolt, so that the pressure on the obstructions could not be detected by 

 feeling. These varieties of locks have been opened by measuring the mo- 

 tion of the bolt b}^ means of a micrometer. Micrometers are made to mul- 

 tiply 20,000 times; so that if the bolt moves a distance equal to the thick- 

 ness of a sheet of tissue paper, the instrument indicates a thickness of 

 20,000 sheets. 



In order to make a secure lock it is necessary to know all of the methods 

 of picking. As soon as lock-makers discover any new method of picking, 

 new devices are introduced to guard against it. The locksmiths thus far 

 have kept far in advance of the burglars in the knowledge of lock-picking; 

 no burglar ever having picked the best lock of the time. 



The ward lock is very ancient; I have seen those that were taken from 

 the ruins of Ilerculaneum and Pompeii, and they were in common use 

 among the Romans. The first lock with movable obstructions was Egyp- 

 tian. There is one in use in Egypt now, which is a very good lock. The 

 bolt is furnished with pins, and the key has pins to correspond, and if the 

 pins are pushed too far into the bolt, those in the key enter the holes and 

 stop the movement of the bolt. 



Mr. Butler. — The Egyptian locks are made of wood, are they not? 



Mr. Hobbs. — Generally of wood, tliough I have seen them of iron. 



The great excitement at the exhibition of 1S51 was caused by the pick- 

 ing of the Bramah lock. As I was walking down Piccadilly I saw a sign 

 in a window which I read as a very fair challenge to pick the lock. I went 

 in and asked the attendant if they would really give 200 guineas to any 

 one who would pick that lock. He replied: 



" Can't you read ?" 



"Yes," said I, "I can read, but I do not believe everything that I read." 



I asked him if he Avould allow me to look at that lock, and he handed it 

 down. I took out my knife and began to feel of the slides, when he inter- 

 rupted me with the remark: 



" If you want to try to pick the lock you can liave a chance at it in a 

 room with our foreman, but you can't be fooling with it here." 



Then a gentleman came forward, and asked me if I was a lockmaker. I 

 told him that I was not, and asked him if they really meant to offer the 

 reward of 200 guineas, according to their placard. He said that they did, 

 when I remarked tliat I should like to have a chance to try it. He said: , 



" Perhaps you did not observe the terms of the card." 



I then examined it more closely, and it read thus: " The artist who will 



