_, 1., which I incline to think is the passage Bacon had
in his mind. The passage quoted from Cicero I merely meant to point out for
comparison.

P. 146.--The passage quoted is from Sen. _ad Lucil._, 52.

P. 147.--_Ad Lucil._, 53.

P. 159.--_Ad Lucil._, 71.

Two or three other passages from Seneca will be found without any
reference. One of them, p. 13., "Quidam sunt tam umbratiles ut putent in
turbido esse quicquid in luce est," I have taken some pains to hunt for,
but hitherto without success. Another noticeable one, "Vita sine proposito
languida et vaga est," is from _Ep. ad Lucil._, 95.

For the reference to Aristotle I am much obliged. I was anxious to trace
all the quotations from Aristotle, but could not find this one.

P. 165.--I cannot answer this question. Is it possible that he was thinking
of St. Augustine? In the _Confessions_, i. 25., we kind the expression
_vinum erroris_.

P. 177.--No doubt Bacon had read the treatise of Sallust quoted, but my
impression is that he thought the proverb had grown out of the line in
Plautus.

P. 180.--I have searched again for "alimenta socordiae," as it is quoted in
the _Colours of Good and Evil_, but cannot fix upon any passage from which
I can say it was taken, though there are many which might have suggested
it. One at p. 19. of the _Advancement_, which I missed at first, I have
since met with. It is from the _Cherson._, p. 106.

THOMAS MARKBY.

* * * * *

PHOTOGRAPHIC CORRESPONDENCE.

_Test for a good Lens._--The generality of purchasers of photographic
lenses can content themselves with merely the following rules when they
buy. It ought to be achromatic, _i. e._ consisting of the usual two pieces
of crown and flint glass, that its curves are the most recommended, and
that it is free from bubbles: to ascertain the latter, hold the lens
between the finger and thumb of the right hand, much as an egg-merchant
examines an egg before a strong gas flame, and a little to the right of it;
this reveals every bubble, however small, and another kind of texture like
minute gossamer threads. If these are too abundant, it should not be
chosen; although the best lenses are never altogether free from these
defects, it is on the whole better to have one or two good-sized bubbles
than any density of texture; because it follows, that every inequality will
refract pencils of light out of the direction they ought to go; and as
bubbles do the