Edit- I just found this confirmation from Smyth-
Correspondence of the Liverpool Post. ALEXANDRIA, Wednesday, May 10, 1865. I have the pleasure now of giving, you the earliest information by letter that I have yet given any one, of the successful taking of photographs under the great pyramid by aid of the light produced when burning the magnesium wire you took so much interest in supplying me with last November. Having had many classes of scientific observations to make at the pyramid, and little skilled assistance. I took them in regular order one after the other, and arranged for trying the magnetism photography last of all; and this is the explanation of my having been so long in giving you any account of the results, or success or non-success of the method. Perhaps, too, I put off the subject rather too long, for being new to me, I required some apprenticeship in working it; and an unexpected opening up of more work took place during the past two weeks we were at the pyramid, and took the very important shape of the four corner sockets on which the pyramid had been originally founded, and which seem to be alluded to in a remarkable passage in the book of Job; and have not all four been seen by men for very many centuries -- being at last excavated and laid open by an enterprising professional man from the West of Scotland. Being, however, thus opened up, I could not but unpack again the astronomical instruments, though they had been prepared for the return voyage home. I make the requisite astronomical observations to prove the relation between these fiducial markings of the original and perfect Pyramid in direction and angle with the present position of the Celestial Pole. Still, notwithstanding the time and labor thus abstracted from the magnesium photography, the powers of that brilliantly burning metal were such as to enable me to secure some very fair negatives of several features of interest in the Grand Gallery and Queen's Chamber, as well as in the King's Chamber. In the latter, the celebrated "coffer" was photographed from a variety of positions, and with the measuring rods arranged about it in the manner proposed by Mr. SIDEBOTTOM; and every subject having been simultaneously photographed in duplicates by two cameras, the full means will be afforded, I trust, with the aid of the stereoscope, of enabling all persons now, whether travelers to the land of Egypt or not, to form a good idea of the proportions and size of that remarkable vessel. At all events, if they do now by such means get a true and satisfactory notion of it, let them thank magnesium and the wholesale manufacturers thereof. C. PIAZZI SMYTH.
Edited 1 time(s). Last edit at 18-Aug-17 22:51 by Apap.