[520]
perpendiculars μν be erected equal to the Radii MN of parallel circles MOM paſſing thro' the correſponding points M of that quadrantal Arc, the greateſt of which βξ let be equal to the Radius BX of the baſe of the Hemiſphere: The figure αβξ will contain the Radii of all the circles of whoſe Peripheries the ſuperficies of the Hemiſphere conſiſts. And if the perpendicular μν, βδ be erected equal to the Peripheries MOM, BDB, there will be made the figure αβδ equal to the ſuperficies of the Hemiſphere. The dimenſion of which figure if you can by any means find (as in this caſe you are to find the Area of the figure αβξ) thence you will eaſily deduce the content of the ſegment of the ſphere, agreeing to what you may gather by any lawful reaſoning. Which Obſervation, I think will not be unuſeful in Geometry.
FINIS.
AT the Hand and Pen in Barbican are Taught, Writing, Common and Merchants Accounts, after that well approved Method of Mr. Normanſel, Algebꝛa, Geometry, Meaſuring, Surveying ,Gauging,Navigation and Dialing, with other parts of the Mathematicks, alſo the Uſe of the Globes, Maps and other Inſtruments, by me
