In designing trussed roofs or bridges, the "primaries" would be invaluable to the engineer, strain-calculations on diagonal and upright members would be simplified, and the builder would find the benefit of a measure in even feet or inches from centre of one pin or connection to another. For earthwork slopes 3, 4, 5; 20, 21, 29; 21, 20, 29; and 4, 3, 5 would be found more convenient ratios than 1 _to_ 1, and 1½ _to_ 1, etc. Templates and battering rules would be more perfect and correct, and the engineer could prove his slopes and measure his work at one and the same time without the aid of a staff or level; the slope measures would reveal the depth, and the slope measures and bottom width would be all the measures required, while the top width would prove the correctness of the slopes and the measurements. To the land surveyor, however, the primary triangle would be the most useful, and more especially to those laying out new holdings, whether small or large, in new countries. Whether it be for a "squatter's run," or for a town allotment, the advantages of a diagonal measure to every parallelogram in even _miles_, _chains_, or _feet_, should be keenly felt and appreciated. This was, I believe, _one_ of the secrets of the speedy and correct replacement of boundary marks by the Egyptian land surveyors. I have heard of a review in the "Contemporary," September, 1881, referring to the translation of a papyrus in the British Museum, by Dr. Eisenlohr--"_A handbook of practical arithmetic and geometry," etc., "such as we might suppose would be used by a scribe acting as clerk of the works, or by an architect to shew the working out of the problems he had to solve in his operations_." I should like to see a translation of the book, from which it appears that "_the clumsiness of the Egyptian method is very remarkable_." Perhaps this Egyptian "_Handbook_" may yet shew that their operations were not so "_clumsy_," as they appear at first sight to those accustomed to the practice of modern trigonometry. I may not have got the exact "hang" of the Egyptian method of land surveying--for I do not suppose that even their "clumsy" method is to be got at intuitively; but I claim that I have shewn how the Pyramids could be used for that purpose, and that the subsidiary instrument described by me was practicable.