261 



perceptible to the human body in its ordinary exposure to the atmo- 

 sphere, and which depends upon the rapidity with which its own 

 heat is carried off by the conducting power and currents of the at- 

 mosphere. To estimate this insensible cold, the author raised the 

 thermometer to 1 20, and then carried it into the open air. As soon 

 as the mercury had fallen to 100, the rate of its further descent, 

 during every 10", was noted for half a minute, in different states of 

 the atmosphere in regard to wind and moisture. These experiments, 

 which are given in the form of tables, show the powerful effect of 

 wind in increasing the rate of cooling, and consequently of exciting 

 the sensation of cold in the human body, independent of any actual 

 low temperature of the atmosphere. 



On the Transit Instrument of the Cambridge Observatory ; being a 

 Supplement to a former Paper. By Robert Woodhouse, Esq. 

 Plumian Professor of Astronomy in the University of Cambridge. 

 Read January 19, 1826. [Phil. Trans. 1826, Part II. p. 75.] 



This communication is intended merely as a supplement to a for- 

 mer 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. 



Account of a Series of Observations, made in the Summer of the Year 

 1825,ybr the purpose of determining the Difference of Meridians of 

 the Royal Observatories of Greenwich and Paris ; drawn up by J. F. 

 W. Herschel, Esq. M.A. Sec. R.S. Communicated by the Board of 

 Longitude. Read January 12, 1826. [Phil. Trans. 1826, Part II. 

 j.77.] 



The operations, of which this paper contains an account, were 

 undertaken by the British Board of Longitude, in conjunction with 

 the French Ministry of War, at the invitation of the latter, for the 

 purpose of connecting the Royal Observatories of Greenwich and 

 Paris, by means of signals contemporaneously observed along a chain 

 of stations established for that purpose between them. The signals 

 employed were the explosions of proper quantities of gunpowder, 

 elevated to a great height in the air by rockets fired at three sta- 

 tions, two on the French, and one on the English side of the Chan- 

 nel, and observed at the observatories, and at two stations interme- 

 diate between those at which thev were fixed. These two stations 



