the invention of lithography, though it was merely
an old German art revived. Even the invention of the penny-postage
system by Sir Rowland Hill is disputed; Dr. Gray of the British Museum
claiming to be its inventor, and a French writer alleging it to be an
old French invention.[14] The invention of the steamboat has been
claimed on behalf of Blasco de Garay, a Spaniard, Papin, a Frenchman,
Jonathan Hulls, an Englishman, and Patrick Miller of Dalswinton, a
Scotchman. The invention of the spinning machine has been variously
attributed to Paul, Wyatt, Hargreaves, Higley, and Arkwright. The
invention of the balance-spring was claimed by Huyghens, a Dutchman,
Hautefeuille, a Frenchman, and Hooke, an Englishman. There is scarcely
a point of detail in the locomotive but is the subject of dispute.
Thus the invention of the blast-pipe is claimed for Trevithick, George
Stephenson, Goldsworthy Gurney, and Timothy Hackworth; that of the
tubular boiler by Seguin, Stevens, Booth, and W. H. James; that of
the link-motion by John Gray, Hugh Williams, and Robert Stephenson.

Indeed many inventions appear to be coincident. A number of minds are
working at the same time in the same track, with the object of
supplying some want generally felt; and, guided by the same experience,
they not unfrequently arrive at like results. It has sometimes
happened that the inventors have been separated by great distances, so
that piracy on the part of either was impossible. Thus Hadley and
Godfrey almost simultaneously invented the quadrant, the one in London,
the other in Philadelphia; and the process of electrotyping was
invented at the same time by Mr. Spencer, a working chemist at
Liverpool, and by Professor Jacobi at St. Petersburg. The safety-lamp
was a coincident invention, made about the same time by Sir Humphry
Davy and George Stephenson; and perhaps a still more remarkable
instance of a coincident discovery was that of the planet Neptune by
Leverrier at Paris, and by Adams at Cambridge.

It is always difficult to apportion the due share of merit which
belongs to mechanical inventors, who are accustomed to work upon each
other's hints and suggestions, as well as by their own experience.
Some idea of this difficulty may be formed from the fact that, in the
course of our investigations as to the origin of the planing
machine--one of the most useful of modern tools--we have found that it
has been claimed on behalf of six inventors--