On the transit instrument of the cambridge observatory; being a supplement to a former paper

This communication is intended merely as a supplement to a former paper on the same subject, printed in the Transactions of this Society, in which a deviation of the transit instrument from the plane of the meridian, arising from a difference of expansion in its braces, was pointed out. As no instance was there given of the magnitude of this deviation, one is here adduced in which the inferior passage of the pole star was found to have been retarded twenty-five seconds in consequence of the sun having been allowed to shine on the up per western brace, the object-glass of the transit being towards the zenith. The author adds, that in consequence of the detection of this source of inequality, he now views with great suspicion all his previous observations of solar transits.