But this work must follow the observations, it could not precede them.  The first step was therefore to observe and to measure with the utmost care the positions and distances of those particular double stars which appear to offer the greatest promise in this particular research.  In 1821, Herschel and a friend of his, Mr. James South, agreed to work together with this object.  South was a medical man with an ardent devotion to science, and possessed of considerable wealth.  He procured the best astronomical instruments that money could obtain, and became a most enthusiastic astronomer and a practical observer of tremendous energy.

South and John Herschel worked together for two years in the observation and measurement of the double stars discovered by Sir William Herschel.  In the course of this time their assiduity was rewarded by the accumulation of so great a mass of careful measurements that when published, they formed quite a volume in the “Philosophical Transactions.”  The value and accuracy of the work, when estimated by standards which form proper criteria for that period, is universally recognised.  It greatly promoted the progress of sidereal astronomy, and the authors were in consequence awarded medals from the Royal Society, and the Royal Astronomical Society, as well as similar testimonials from various foreign institutions.

This work must, however, be regarded as merely introductory to the main labours of John Herschel’s life.  His father devoted the greater part of his years as an observer to what he called his “sweeps” of the heavens.  The great reflecting telescope, twenty feet long, was moved slowly up and down through an arc of about two degrees towards and from the pole, while the celestial panorama passed slowly in the course of the diurnal motion before the keenly watching eye of the astronomer.  Whenever a double star traversed the field Herschel described it to his sister Caroline, who, as we have already mentioned, was his invariable assistant in his midnight watches.  When a nebula appeared, then he estimated its size and its brightness, he noticed whether it had a nucleus, or whether it had stars disposed in any significant manner with regard to it.  He also dictated any other circumstance which he deemed worthy of record.  These observations were duly committed to writing by the same faithful and indefatigable scribe, whose business it also was to take a memorandum of the exact position of the object as indicated by a dial placed in front of her desk, and connected with the telescope.

John Herschel undertook the important task of re-observing the various double stars and nebulae which had been discovered during these memorable vigils.  The son, however, lacked one inestimable advantage which had been possessed by the father.  John Herschel had no assistant to discharge all those duties which Caroline had so efficiently accomplished.  He had, therefore, to modify the system of sweeping previously