254 SPECULATIVE SCIENCE 



patent ? At first sight nothing can be more different than the 

 drawing in the patent and the machine produced in court, and 

 yet counsel and witnesses shall prove to the satisfaction of 

 judge, jury, and one party to the suit, that the essential part, the 

 important organ, is the same in both cases. The case will often 

 hinge on the question, What is the important organ ? Just the 

 question which Darwin asks ; and quite as difficult to answer 

 about a patented machine as about an organic being. 



This difficulty results from the action of man's mind con- 

 triving machines to produce a common result according to defi- 

 nite laws, the laws of mechanics. An instance of this is afforded 

 by the various forms of bridge. Nothing would appear more 

 distinct than the three forms of suspension bridge, girder, and 

 arch ; the types of which are furnished by a suspended rope, a 

 balk of wood, and a stone arch ; yet if we substitute an iron- 

 plate girder of approved form for the wooden balk, and then a 

 framed or lattice girder for the plate-iron girder, we shall see 

 that the girder occupies an intermediate place between" the two 

 extremes, combining both the characteristics of the suspension 

 and arched rib the upper plates and a set of diagonal strutts 

 being compressed like the stones of an arch, the lower plates 

 and a set of diagonal ties being extended like a suspended rope. 

 Curve the top plates, as is often done, and the resemblance to 

 an arch increases, yet every member of the girder remains. 

 Weaken the bracing, leaving top and bottom plates as before, 

 the bridge is now an arched bridge with the abutments tied 

 together. Weaken the ties gradually, and you gradually ap- 

 proach nearer and nearer to the common arch with the usual 

 abutments. Quite similarly the girder can be transformed into 

 a suspension bridge by gradual steps, so that none can say 

 when the girder ends and the suspension bridge begins. Nay, 

 take the common framed or lattice girder, do not alter its shape 

 in any way, but support it, first, on flat stones like a girder, then 

 wedge it between sloping abutments like an arch, and lastly, 

 hang it up between short sloping links like those of a suspension 

 bridge, attached to the upper corners at the end you will so 

 alter the strains in the three cases that in order to bear the 

 same load, the relative parts of the framework must be altered 

 in their proportions in three distinct ways, resembling in the 



