Sentence:  As was observed before in Figuration of Surds; so here it may be remembred that any Species simply Irrational, multiplied <WSD>figurately</WSD>, produceth a Rational: But Compound Irrational Species may be squared, cubed, etc. by multiplying them <WSD>figurately</WSD> as other Figural Numbers are multiplied; but the Unciae to the Parodical Degrees here, will be the Squares of them in Rational Species. 
Meaning of the word marked with <WSD> tags:  In a figurate manner; Using or forming a figure.