_Mr. Sisson's developing Fluid._--Since I sent you the new formula for MR.
SISSON'S positive developer, which you published in Vol. viii., p. 301.,
MR. SISSON has written to me to say that if, instead of the acetic acid,
you add two drachms of formic acid, the new agent proposed by MR. LYTE, you
certainly obtain the sweetest-toned positives he has ever seen. The
pictures, he says, come out very quickly with it indeed; and with a small
lens in a sitting-room he can in about ten seconds obtain the most
wonderful detail. Every wrinkle in the face, and ladies' lace ribbons or
cap-strings, he says, come out beautifully.