98 Generating Economic Cycles 



We come now to the second part of our question: is 

 there reason for beUeving that the Venus cycle is accom- 

 panied with a synchronously varying force which could 

 produce the observed meteorological cycles? Here our 

 point of departure is a comparatively recent discovery 

 of great importance relating to the period of rotation of 

 Venus upon its axis. 



From the observations of some faint markings sup- 

 posedly on the surface of Venus, Domenico Cassini of 

 Bologna in 1666-67 inferred that the period of rotation 

 was about twenty-three hours. J. J. Cassini, in 1740, 

 gave a more exact estimate of twenty-three hours and 

 twenty minutes. Schroeter, in 1789, fixed the period at 

 twenty-three hours and twenty-one minutes, and De 

 Vico, in 1839-41, carried the spurious accuracy to 

 twenty-three hours, twenty-one minutes, and twenty- 

 two seconds. So the matter remained until 1890, when 

 Schiaparelli announced his surprising discovery, 



Schiaparelli made the innovation of conducting his 

 observations by day, as near to noon as possible, when 

 Venus would be highest and its own glare reduced by the 

 brilliant midday sky. From a long series of careful 

 observations he concluded that the period of rotation 

 of Venus upon its axis could be nothing like twenty- 

 four hours, but must lie between six and nine months 

 and very probably agreed exactly with its period of 

 revolution around the Sun, which is, approximately, 

 225 days. 



In 1896 the question was made the subject of research 

 by Percival Lowell with the assistance of an accom- 

 plished staff, at his observatory in the clear air of Flag- 

 staff, Arizona. The markings noted by Schiaparelli 



