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 centres of each of these pulleys are made to revolve in periods which are determined by the movements of the sun and moon. When the machine is to be employed for predicting the tides in any particular port, the positions of all these pulleys must be set so to speak in conformity with certain individual circumstances connected with the particular port—thus, though the tides at Madras are totally different from the tides at London Bridge, yet the same machine may be used to calculate both. The fundamental movements of the machine are constant for all ports, but the various pulleys will in the one case have to be set in conformity with the local conditions of Madras, and in the other case they would have to be set in conformity with the local conditions of London Bridge. Two totally distinct tide-tables, appropriate however to the two ports named, could thus be generated by the revolutions of this useful machine.

It would perhaps be too much to anticipate that the time will ever come when meteorological phenomena shall admit of being worked out by a machine on the principle of the tide-predicting engine. But yet it does not seem altogether vain to strive for such a result. We can, in fact, give some reasons for indulging a hope that something of this kind may yet be accomplished. In the first place it is perfectly clear that the radiation of heat from the sun must be the chief factor in the variations of all meteorological quantities. The fluctuations of temperature with the changing seasons are among the most obvious instances of the connection between the sun and the climate, but it may be shown that the changes of every other meteorological element are also primarily dependent on the sun.