Note 25 — Chapter III

Messrs. Ross have two series of eye-pieces, both Huyghenian. One series is for use with the English 10-inch tube-body, and is distinguished by Roman letters, and the other by numerals, and made as is usual on the Continent, and for use with the shorter tube-body 6½-inch. The initial powers given in the table are for the 10-inch tube, and for the shorter must be read as follows:—

1 2 3 4 } with 6½-inch tube.

4 6 8 12 }