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 adopted in order to enable all the work both of
observing and of recording to be done by himself. This, in many
ways, was a great drawback to the work of the younger astronomer. The
division of labour between the observer and the scribe enables a
greatly increased quantity of work to be got through. It is also
distinctly disadvantageous to an observer to have to use his eye at
the telescope directly after he has been employing it for reading the
graduations on a circle, by the light of a lamp, or for entering
memoranda in a note book. Nebulae, especially, are often so
excessively faint that they can only be properly observed by an eye
which is in that highly sensitive condition which is obtained by long
continuance in darkness. The frequent withdrawal of the eye from the
dark field of the telescope, and the application of it to reading by
artificial light, is very prejudicial to its use for the more
delicate purpose. John Herschel, no doubt, availed himself of every
precaution to mitigate the ill effects of this inconvenience as much
as possible, but it must have told upon his labours as compared with
those of his father.
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