56 



chiefly of a-continuation of his observations on the appearances of 

 that body from the 2nd of March to the 3rd of May last. 



Conceiving that there might be some advantage in getting rid of 

 the darkening glasses in viewing the sun, he was led to substitute for 

 them various liquors, such as spirits of wine, port wine, ink diluted 

 with water, a solution of green vitriol with a small proportion of 

 tincture of galls, and even plain water ; which latter he found keeps 

 off the heat so effectually, that the brightest sun may be viewed some 

 time through it without any inconvenience. 



Through diluted ink, the image of the sun appeared as white as 

 snow ; and when the liquor was still more diluted, the sun was of a 

 purple hue, while the objects on its surface continued as distinct as 

 when seen through any other medium. From these observations the 

 author infers that the continuance of the symptoms which in his 

 former paper he considered as favourable to the copious emission of 

 light and heat from the sun, are sufficiently verified, and that by 

 comparing these phenomena with the corresponding mildness of the 

 season, his arguments respecting the connexion between them and 

 the temperature of our atmosphere acquire no small degree of pro- 

 bability. 



Being well aware that the price of wheat which he adopted in his 

 former paper as a criterion of the seasons is liable to some objections, 

 the author desires here to be understood, that his intention was 

 merely to compare the astronomical fact of the variable emission of 

 the sun's rays with the obvious symptoms corresponding with that 

 circumstance ; leaving it to others to apply the subject to such use- 

 ful ceconomical purposes as may be found to have any relation to 

 them : at any rate, he cannot relinquish the hope that astronomy will 

 ultimately supply us with the means of deriving certain prognostics 

 of the temperature of the seasons from accurate observations on the 

 quantity of the light we receive from the sun. 



On an improved Reflecting Circle. By Joseph de Mendoza Rios, Esq. 

 F.R.S. Read June 4, 1801. [Phil. Trans. 1801,^. 363.] 



The great utility of Hadley's quadrant in practical astronomy, and 

 particularly in navigation, has given rise to several improvements of 

 that valuable instrument, of which some account is premised in the 

 present paper. The first of these is due to the celebrated Tobias 

 Meyer, who, by completing the limb of the sextant into a whole 

 circle, and adding an horizon index, enabled us to repeat the obser- 

 vations, so as to ascertain the double, triple, and even a greater 

 multiple of the angles ; by which means the errors of division or 

 eccentricity in the instrument can be reduced in the inverse ratio of 

 the repetition of the observations, so as to arrive at any degree of 

 approximation that may be required. 



Some imperfection still remaining as to the manner of rendering 

 the glasses parallel, so as to produce the exact coincidence of the 

 images, the Chevalier de Borda contrived a method of rendering this 

 exact parallelism of less consequence, by substituting the immediate 





