The balancing of the series of forces will not be complete until the respective **triplets** of conjunctions have filled up the entire space between them.

**Triplets** are employed when the focal length of the simple microscope was less than in.

**Triplets**, quadruplets, &c., be made with n symbols, so that (1) every contiguous pair of symbols in one multiplet are a contiguous pair in some other, the first and last of any multiplet being considered contiguous, and (2) no three symbols in any multiplet shall occur in any other.

Hamilton, still keeping prominently before him as his great object the invention of a method applicable to space of three dimensions, proceeded to study the properties of **triplets** of the form x+iy+jz, by which he proposed to represent the directed line in space whose projections on the co-ordinate axes are x, y, z.

Strontium also gives **triplets**, but only the side branch series has been observed.

If a is the distance shown by the normal **triplets** the type of separation observed in the line D2 shows distances from the central line equal to a /3, 3a/3, 5a/3, while the type of D 1 gives 2a/3, 4a/3.