80 PHILOSOPHICAL TRANSACTIONS. [aNNO 1673« 



Speculation on the centres of agitation, or oscillation, in which occur many con- 

 siderable theorems, relating to linear, plain and solid figures. 



To all which he promises the mechanical structure of the watch, and the ap- 

 plication of the pendulum to it ; enriching that part with his table of the equa- 

 tion of days, as also with a relation of the several successes of such watches 

 employed in considerable sea- voyages; of which he says the best of all has been 

 that in the expedition of the late Duke of Beaufort into Candia ; who, having 

 taken with him in his own ship two of those watches, and appointed a good 

 astronomer to take care of them ; the longitudes of the places, which they either 

 touched at in that voyage, or which in passing by they could see, were by 

 means of the said watches exactly measured, so as that the very same differences 

 of longitudes were found by the most accurate maps assigned to those places. 



But since those trials, our author says he has improved his watches, by using 

 a pendulum of a triangular figure, and by another way of suspending them ; of 

 which he gives an ample description. We may also notice his universal and 

 perpetual measure, which he establishes by exactly taking the measure of the 

 distance from the point of suspension to the centre of oscillation of a simple 

 pendulum vibrating a second of time ; which being found to be such a length, 

 as being divided into three equal parts, will make such a measure, as he calls an 

 horary foot ; which having such or such a proportion to all other feet, may be 

 used to settle a constant and certain measure every where, and to recover it in 

 all ages, as time will be always and in all places the same ; and consequently such 

 a length being taken as exactly equals a second of time, a just universal measure 

 is obtained. 



II. Modern Fortification, &c. ; by Sir Jonas Moore,* master surveyor of 

 his Majesty's ordnance. Lon. 1673, in 8vo. 



* Sir Jonas Moore, F. R. S. was a respectable matliematiclan, besides a good engineer, and be- 

 came surveyor general of the ordnance, or master surveyor as it was then officially called. He was 

 born at Whitbee, near the confines of Lancashire and Cheshire, about the year l6l5, and enjoyed 

 a liberal education, but bent his studies chiefly to the matliematics and astronomy, to which he was 

 always strongly attached. In the expeditions of King Charles the 1st in the northern parts of Eng- 

 land, Mr. Moore was introduced to him, as a person learned in those sciences j which laid the 

 foundation of his fortune. In l647 he was appointed mathematical preceptor to the king's second 

 son, James the Duke of York. During Cromwell's government it seems he followed tlie profession 

 of a public teacher of mathematics, when his loyalty was a great prejudice to his fortune. After the 

 return of Charles the lid, he found great favour both with the king and duke of York, who often 

 consulted him, and were advised by him on many occasions. And it must be owned that he used to 

 employ his interest with the court to the advancement of learning and the encouragement of merit. 

 Thus, he procured the royal observatory at Greenwich to be built in l675, recommending Mr. 

 Flamsteed as the king's astronomer there. Also, being a governor of Christ's Hospital, by his in- 

 terest the king founded the mathematical school tliere : and for the use of tliis school Sir Jonas com- 



