by any trustworthy historical evidence.

[Footnote 3: Janus, 1903, p. 20.]

The "_Liber de speculis_" mentioned by Gilbert (f. 126 c), and since
the time of Freind generally accepted as the work of Bacon, is almost
certainly not from the pen of that eminent philosopher. In addition
to the fact that Bacon himself says he had (for obvious reasons)
written nothing except a few tracts (_capitula quaedam_) prior to the
composition of his Opus Magnum in 1267, the real author of the Liber
de speculis is probably mentioned by Bacon in the following passage
from the Opus Tertium:

"_Nam in hoc ostenditur specialiter bonitas naturae, ut dicit auctor
libri de speculis comburentibus._"[4]

[Footnote 4: Cap. XXXVI, p. 116, edition of Brewer.]

We must therefore agree with Dr. Payne that the _Liber de speculis_ of
Gilbert was at least not the work of Roger Bacon.

Dr. Freind regards the chapters of Gilbert on the subject of leprosy
as borrowed substantially from the "Chirurgia" of Theodorius of
Cervia, who wrote about the year 1266. This view has also been
generally accepted by later writers. But Dr. Payne boldly challenges
the view of Freind, declares that Theodorius copied _his_ chapters
from Gilbert, and asserts that Theodorius was a notorious plagiarist.
Now, while the bold assertion of Dr. Payne cannot, of course, be
accepted as _proof_ of Gilbert's precedence in chronological order,
if that precedence is otherwise established, it will explain the