dehors qui respondent a ce trou, auquel il faut mettre un verre
convexe. On a souhaite, pour donner plus d'agrement a ce spectacle, que
les objets se peignissent sur ce papier selon leur veritable situation;
et pour cet effet on a cherche des expediens qui redressassent les
especes avant qu'elles parvinssent au foier du verre, c'est-a-dire, sur
le papier. L'auteur raporte '10' de ces expediens, et trouve dans
chacun d'eux quelque chose d'incommode, mais enfin il en raporte un
autre, qui est exempt de toutes ces incommoditez, et qui, par le moien
d'un prisme, au travers duquel il faut regarder les images peints sur
le papier, les montre dans leur situation droite, et augmente meme la
vivacite de leurs couleurs. C'est le hazard qui a decouvert ce
phenomene."

This letter is to be found at length in the _Miscellanea Curiosa, sive
Ephemeridum Medico-Physicarum Germanicarum Academiae Naturae curiosorum
decuria II. annus quartus, anni 1685 continens celeberrimorum Virorum
observationes medicas_: Norimbergae, 1686, in 4to. It may perhaps be worth
consulting, if it were only to know what the ten rejected expedients are.

ANON.

_Queries on Dr. Diamond's Collodion Process._--Will you oblige me by
informing DR. DIAMOND through your valuable publication, that I am, in
common with many others, extremely indebted to him for his collodion, and
would esteem it a favour if he would answer the following Queries, viz.:

1st. He says, in answer to a previous Query, that "nitrate of potassa" is
_not_ formed in his process. Now I wish to ask if (as the iodide of silver
is redissolved in iodide of potassium) it is _not_ formed when the plate is
plunged into the nitrate silver bath, as the nitrate decomposes the iodide
of potassium?

2nd. How long will the collodion, according to his formulae, keep, as
collodion made with iodide of silver generally decomposes quickly.

3rdly. Why does he prohibit _washed_ ether?

4thly. Does he think cyanide of potassium would do as well as the iodide,
to redissolve the iodide of silver, iodide of potassium being at present so
dear?

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5thly. In his paper process, does not the soaking in water after iodizing
merely take away a portion of iodides of silver and potassium from the
paper; or, if not, what end is answered by it?

W. F. E.

_Baths for the Collodion Process._--Having lately been assured, by a
gentleman of scientific attainments, that the s