556 Chronicles of Science. [Oct., 



cylinder, the air is compressed in a similar manner, and the cylinder 

 is forced down by the compressed air between the piston and cylin- 

 der bottom, until the stamp-head strikes the ore in a coffer-trough ; 

 thus, whether the quantity of ore be large or small, the blow is 

 always effective, the only difference in the working of the machine 

 being a shorter or longer vertical play of the cylinder and head. 



The committee appointed by the North of England Institute of 

 Mining Engineers to investigate the action of safety cages and 

 hooks have made their report. After a most careful investigation 

 of all the inventions which were brought before them, and they 

 were very numerous, they have arrived at the following conclusion : — 

 " That there are really but two different classes, namely, those which 

 come into operation every time the chain is slackened, and those 

 which do so only when the cage is actually falling or descending at 

 a speed almost equal to that of a falling body. Inventions of the 

 first class are very numerous ; the second class has one sole expo- 

 nent, Calow, and both depend on the action of springs (which are 

 always subject to derangement) to initiate the grip, which intensi- 

 fies itself by being drawn more and more into gear by friction on 

 the guides. Both systems have their advantages and disadvantages ; 

 for even Calow's, although it does not wear so much as the others 

 by being constantly in motion at the top and bottom of the pit, yet 

 is apt to stick in the shaft if by any cause the cage receives a 

 sudden jerk." 



In conclusion the committee say : — " It must be admitted that, 

 with every desire to see some efficient apparatus in use at every 

 colliery to prevent the lamentable loss of life that occasionally occurs, 

 your committee have felt an instinctive distrust of the various modes 

 hitherto proposed for doing so, which distrust has not been alto- 

 gether overcome by the investigation that has been gone into. Up 

 to the present time there seems some element wanting to perfect these 

 machines (some of which are excessively ingenious) and render them 

 really reliable, and it is much to be desired that such an improvement 

 may be arrived at speedily. With this feeling your committee can- 

 not express an opinion as to the necessity for the adoption of any 

 of these provisions for safety, and can only lay before you the facts 

 they have acquired, with such deductions from statistics and obser- 

 vations as have presented themselves, and which it is hoped will 

 materially assist in considering the merits of new inventions." 



Papers on the Theory and Practice of Coal Mining. By 

 George Fowler, M.E. W. M. Hutchings. London.— Mr. Fowler 

 has read before the Institution of Civil Engineers, and other 

 societies, papers " On the Kelative Safety of different Modes of 

 Working Coal," and on kindred subjects. These papers are now 

 gathered together, and, reconstructed, are presented to the public 

 in a very useful form. Each mode of working coal is carefully 



