No. 151.] 185 



when leisure permits. But it is usual, nevertheless, to have others in 

 attendance, and the machine rings a small bell to give notice. 



The great merit of this invention of Professor Morse, consists in 

 dispensing with all the conducting wires but one, by which the cost 

 has been reduced within the convenient reach of individual means. 

 Had no other plan but Professor Wheastone's been discovered, the 

 beautiful phenomena would have been confined to the slow and cau- 

 tious advance of governments, and its practical advantages would 

 have been retarded and kept buried up for half a century. 



The idea of making the earth a part of the circuit, the return 

 conductor, was the discovery of a philosopher, the results of which 

 we have not fully calculated. The proposition a few years since to 

 send along a thought upon a flash of lightning, or of communicating" 

 the same in any form by means of electricity, would have been con- 

 sidered a great absurdity — the offspring of unmingled insanity in the 

 proposer. 



There are other machines, and improvements in machines, which 

 might be named in the catalogue of machines, auxiliary to the se- 

 condary wants of man; but to name them, would be but to reiterate 

 a general progress already noticed in those which have been named, 

 about one hundred in number, which have appeared within the last 

 one hundred years; in the aggregate, they have advanced the objects 

 for which they have been made, at least one hundred fold; and that 

 of all that has been named, at least one-half are wholly dependant 

 upon cam motions for their existence and operation. 



This being the case, no farther argument is necessary to prove the 

 important bearings and usefulness of the cam motion in the construc- 

 tion of labor-saving machinery. 



But the question may arise in some minds, what is a cam ? what 

 does it look like? by what feature shall we distinguish it, when we 

 "view it in a machine? 



How is it, that people in general know so little about it? is not 

 the term a vulgarism? 



The only answer we can give to the inquiry, is, that the name is 

 of course a technical term, to express a part in the construction of 

 machines; that the word occurs of a necessity, in a minute descrip- 

 tion of machinery, and may be met with in vocabularies of mechani- 

 cal terms; but that a critical definition of the word, does not exist in 



