E Stadia points for clamp and tangent levels.
F Stadia points for ordinary levels.
G Stadia glass diaphragm.
H Webs.
J Stadia webs.
Fig. 83.
Larger image
241.—The further discussion of the subject of high-class levels becomes somewhat difficult. Leaving out of consideration the levels sold by the trading optician, who deals in the commercial article but sometimes superadds a little fad, every genuine manufacturer has his pet plans of carrying out details, some of which may be very meritorious, but which could scarcely be described without a fuller discussion than our space permits. There is also, no doubt, a great number of mistakes that have been made in the construction of surveyor's levels. The direction in which the scientific optician generally fixes his attention is to give the advantages of the Y-level in the dumpy form, assuming the civil engineer holds a certain amount of prejudice against the use of the Y, for which, in its old form at least, the writer must admit that he was fully justified. Whether the professional man, nevertheless, will ever depart from the solid construction of the dumpy remains an open question.
Fig. 84.—Cushing's 12-inch improved level.