20 NATURAL INHERITANCE. [CHAP. 



the subject of patent rights ; at the same time it need 

 not be so minutely defined as to exclude the possibility 

 of small improvements or of deviations from the main 

 design, any of which may be freely adopted by the in- 

 ventor without losing the protection of his patent. But 

 the range of protection is by no means sharply distinct, 

 as most inventors know to their cost. Some other man, 

 who may or may not be a plagiarist, applies for a sepa- 

 rate patent for himself, on the ground that he has intro- 

 duced modifications of a fundamental character ; in other 

 words, that he has created a fresh type. His application 

 is opposed, and the question whether his plea be valid 

 or not, becomes a subject for legal decision. 



Whenever a patent is granted subsidiary to another, 

 and lawful to be used only by those who have acquired 

 rights to work the primary invention, then we should 

 rank the new patent as a secondary and not as a 

 primary type. Thus we see that mechanical inventions 

 offer good examples of types, sub-types, and mere 

 deviations. 



The three kinds of public carriages that characterise 

 the streets of London ; namely, omnibuses, hansoms, 

 and four-wheelers, are specific and excellent illustra- 

 tions of what I wish to express by mechanical types, 

 as distinguished from sub-types. Attempted improve- 

 ments in each of them are yearly seen, but none have as 

 yet superseded the old familiar patterns, which cannot, 

 as it thus far appears, be changed with advantage, taking 

 the circumstances of London as they are. Yet there 

 have been numerous subsidiary and patented contriv- 



