Page:Philosophical Transactions - Volume 145.djvu/140

124 Cairo was afterwards added, with the necessary instruments, to make plans and sections and to take the levels of the ground. Twenty Bedouin labourers were also engaged.

Eight pits or excavations were sunk around the obelisk at different distances, in the situations indicated in the annexed ground plan, and they were carried down to the lowest level of the waters of infiltration in the Heliopolis district on the 16th of July.

Fig. 3. Relative situations of the pits at Heliopolis.

[The figures indicate the distances in yards between the pits.]

Before beginning to describe the several excavations it will make the descriptions of them more intelligible and will save repetitions, if I give an account of the nature of the soils sunk through.

As it was to be expected that, on the same level, and within a space of moderate extent, there would be an identity of composition, I requested to send me specimens of all the varieties of soil he met with in sinking the pits, he himself keeping corresponding specimens; thus establishing a standard to refer to in his reports, and saving the necessity of sending specimens of identical alluvia. My request however was not made until he was carrying on similar researches in the district of Memphis, and they were selected from his excavations there; but they have equally served as a standard of comparison for the soils sunk through at Heliopolis, samples of which were in my possession when I made the request.

All the Nile mud, properlyso called, has at one time or other been suspended in its water. I was therefore desirous that an experiment should be made to ascertain the quantity of solid matter held in suspension in the water, at a given place near Cairo. Having communicated my wish to Mr., he prevailed upon Dr. ,a physician long resident at Cairo, to undertake the inquiry. I then described the process and apparatus by which I had in the year 1832 ascertained the amount