382 Astronomy and Photography at Rome. 



coming piety, stoutly sustained his father's good fame. But all 

 would not do : the northern astronomers would not believe that 

 any spots could be any where seen in Venus, for they were invi- 

 sible at Paris and London. Cassini found himself in the predic- 

 ament of Fontana, and the story of the man of Rhodes must 

 have haunted his recollection. 



Yet still there were intimations from time to time given by 

 astronomers at Rome, that they did see spots as Cassini had seen 

 them ; and at last Francisco Bianchini, in 1726, gave a map of 

 the planet and his estimate of its rotation, which he made to be 

 nearly 24 days, 8 hours. Now the time of the true rotation, as 

 ascertained by the authors of the memoir now produced, is 23 

 hours, 21 minutes, 22 seconds ; and 25 of those rotations would 

 take up in time 24 days, 7 hours, 54 minutes, 8 seconds, so that 

 the theory propounded by Bianchini may be regarded as a com- 

 promise offered to those opposed to Cassini. The matter remain- 

 ed thus, in the slumber of doubt, for more than a hundred years, 

 for the opinions of Schroter were merely an adoption of those of 

 Cassini, although Lalande, Delambre, and Laplace repeatedly 

 urged the necessity of constant observation in the southern obser- 

 vatories, for the solution of so important a problem ; and it is only 

 lately that, younger men having succeeded to the direction of 

 the Roman observatory at the Collegio Romano, and having 

 their lives before them, the matter has been taken in hand in 

 earnest. 



The methods used have been those particularized by Delam- 

 bre, combining the known orbitual movements of the earth and 

 of the planet, with the diurnal changes of position observed 

 in the spots. For three years the observations made have been 

 incessant; between January 1, 1840, and April 30, 1840, they 

 amounted to one thousand six hundred and fifty in number. 

 Designs of the apparent discs of the planet were taken several 

 times a day. Of these ninety one are given with the memoir; 

 the general map is to follow. The result of the whole is com- 

 pletely confirmatory of the statements and calculations of Cassini 

 as far as regards the time of the rotation, and of the accuracy, in 

 a great degree, of the map published by Bianchini. The error 

 of Bianchini in his estimate of the rotation appears to be owing 

 to his having mistaken the return of certain spots for those of oth- 

 ers, and to his having founded his theory on too limited a num- 

 ber of observations. 



