Secondly, That this Volume is divided into two Parts, whereof the First is composed of Ten Books; in which the Author
considers the principal Observations, hitherto made of the Motion of the Planets and the Fixed Stars, of their Magnitude, Figure, and other Accidents; drawing thence several Conclusions, in which he establishes his Hypothesis. The second contains his Astronomical Tables, made according to the Hypotheses of the First Part, together with Instructions teaching the manner of using them.
Thirdly, That Astronomers will find in this Book many very remarkable things, concerning the Apparent Diameter of the Sun and the other Stars, the Motion of the Libration of the Moon, the Eclipses, Parallaxes, and Refractions: And that this Author shews, that there is a great difference between Optical and Astronomical Refraction, which Tycho and many others have confounded; undertaking to prove, that, whereas these Astronomers have believed, that the remoter any Star is, the less is its Refraction, on the contrary the Refraction is the greater, the more a Star is distant. And among many other things, he ingeniously explicates the two contrary Motions of the Sun, from East to West, and vice versa, by one onely Motion upon a Spiral, turning about a Cone.
Fourthly, That he represents, How uneasie it is to establish sure Principles of this Science, by reason of the difficulties of making exact Observations. So, for example, in the Observation of the Equinox, every one is mistaken by so many Hours, as he is of Minutes, in the Elevation of the Pole, or the Diameter of the Sun, or the Refraction, or in any other circumstance. In the Observation of the Solstice, the error of one only Second causeth a mistake of an Hour and an half: mean time 'tis almost impossible to avoid the error of a Second; and even the sharpest sight will not be able to perceive it, except it be assisted with an Instrument of a prodigious bigness. For to mark Seconds, though Lines were drawn as subtil as the single threds of a Silk-worms Clew, (which are the smallest spaces to be discerned by the sharpest Eye) by the Calculation made by this Author there would need an Instrument of 48. feet Radius, since Experience shews, that there needs no more at most, than 3600. threds of Silk to cover the space of an inch. But, suppose one could have a Quadrant of this bigness, who can assure himself, that dividing it into
324000. parts (for so many Seconds there are in 90. Degrees) either in placing it, or in observing, he shall not mistake the thickness of a single thred of Silk? He adds, that Great Instruments have their defects, as the small ones: For in those, that are Movable, if the thred, on which the Lead hangs, is any thing big, it cannot exactly mark Seconds; if it be very fine, it breaks, because of its great length, and the weight of the Lead: And in the Fixed ones, the greater the Diameter is, the less the Shadow or the Light is terminated; so that it is painful enough, exactly to discern the extremities thereof. Yet 'tis certain, that the greater the Instruments are, the surer Astronomers may be: Whence it is, the some Astronomers have made use of Obelisks of a vast bigness, to take the Altitudes; and Signior Cassini, after the example of Egnatio Dante, caused a hole to be made on the highest part of a Wall of 95. feet in a Church at Bononia, through which the beams of the Sun falling on the Floor, mark as exactly as is possible, the height of that Luminary.
Fifthly, That the Author reasons for the Immobility of the Earth after this manner. He supposes for certain, that the swiftness of the Motion of heavy bodies doth still increase in their descent; to confirm which principle, he affirms to have experimented, That, if you let fall a Ball into one of the Scales of a Ballance, according to the proportion of the height, it falls from, it raiseth different weights in the other Scale. For example, A Wooden Ball, of 1½ ounce, falling from a height of 35 inches, raiseth a weight of 5. ounces; from the height of 140 inches, a weight of 20 ounces; from that of 315 inches, one of 45 ounces; and from another of 560 inches, one of 80 ounces, &c. From this principle he concludes the Earth to be at Rest; for saith he, if it should have a Diurnal Motion upon its Center, Heavy Bodies being carried along with it by its motion, would in descending describe a Curve Line, and, as he shews by a Calculus, made by him, run equal spaces in equal times; whence it follows, that the Celerity of their Motion would not increase in descending, and that consequently their stroke would not be stronger, after they had fallen thorow a longer space.
III. ANATOME MEDULLAE SPINALIS, ET NERVORUM inde provenientium, GERARDI BLASII, M. D.
The Author shews in this little Tract a way of taking the entire Medulla Spinalis, or Marrow of the Back, out of its Theca or Bony Receptacle without Laceration; which else happens frequently, both of the Nerves proceeding from it, and of the Coats investing it; not to name other parts of the same. This he affirms to have been put into practice by himself, by a fine Saw and Wedge; which are to be dexterously used: and he produceth accordingly in excellent Cuts, the Representations of the Structure of the said Medulla thus taken out, and the Nerves, thence proceeding; and that of several Animals, Dogs, Swine, Sheep.
He intermixes several Observations, touching the Singleness of this Medulla, against Lindanus and others; its Original; vid. Whether it be the Root of the Brain, or the Brain the Root of it: its difference of Softness and Hardness in several Animals; where he notes, that in Swine it is much softer than in Dogs, &c.