Twenty-five Feet Research Articles

VIII. Continuation of a former paper on the twenty-five feet zenith telescope lately erected at the Royal Observatory

During the last summer I had the honour of submitting to this Society a short paper on the subject of the large zenith telescope lately erected at this Observatory. It is now nearly twenty years since the erection of such an instrument was first suggested to the President and Council of this Society; at that time the Royal Ob­servatory was in a very inefficient state compared to what it is at present. We had only one circle; and there existed doubts as to the excellence of this instrument, though not any were ever entertained by me. The erection of a second circle put this question at rest; it has been abundantly shown in various volumes of the Greenwich Observations, by a series of more rigorous investigations than any instrument was ever submitted to before, that both the circles may be considered as perfect, their errors being less than their respective makers themselves assigned.

XXI. An account of the meteorological instruments used at the Royal Society's house.

<italic>Of the thermometers, with reflections concerning some precautions necessary to be used in making experiments with those instruments, and in adjusting their fixed points</italic>. The thermometers are both adjusted to Fahrenheit's scale: that without doors is placed out of a two-pair-of-stairs window, looking to the north, and stands about two or three inches from the wall, that it may be the more exposed to the air, and the less affected by the heat and cold of the house. The situation is tolerably airy, as neither the buildings opposite to it, nor those on each side, are elevated above it in an angle of more than 12°; but as the opposite building is only twenty-five feet distant, perhaps the heat may be a little increased at the time of the afternoon observation by the reflection from thence.