VOL. LXIV.] PHILOSOPHICAL TRANSACTIONS. 487 



We often find Scheiner and Hevelius mentioning many things concerning the 

 spots, which appeared to them very inexphcable. Hevelius, when speaking of 

 the vast number of spots which break out upon the sun, and of the prodigious 

 size of some of them, admires how from his single body so much matter, exha- 

 lations, &c. could be generated, as in any degree to be adequate to so many and 

 so vast phenomena. Now every theory, how ingenious soever, which is founded 

 on a misapprehension of things, is apt to be pressed with many difficulties; and 

 whenever palpable contradictions appear, they may be regarded as proofs of our 

 having fallen into error. It must indeed be acknowledged, that it is very disad- 

 vantageous to science, to indulge much in hypotheses, the truth being rarely hit 

 upon in this way, and very often missed. Sometimes however it may not be 

 improper to throw out hints and conjectures, when we can attain to nothing 

 better, provided we are at due pains to distinguish between such, and that real 

 knowledge which we derive, by strict induction, from incontestable principles. 

 The best way therefore, of preserving so proper and necessary a distinction, will 

 be to propose what further remains to be said on this subject, in the form of 

 queries ; because, however plausible they may appear, they are at best but matter 

 of conjSfture. Hints, when propounded in this way, are freed from the danger 

 of making us rest in any error, while, sooner or later, they may become helps in 

 leading us to a right understanding of the subject. 



The queries which Dr. W. makes, are chiefly founded on the following phe- 

 nomena of the spots, as described by Scheiner and Hevelius. 1. Every spot 

 which has a nucleus, has also an umbra surrounding it. 2. The boundary be- 

 tween the nucleus and umbra is always distinct and well defined. 3. The in- 

 crease of a spot is gradual, the breadth of the nucleus and umbra dilating at the 

 same time. 4. In like manner the decrease of a spot is gradual, the breadth of 

 the nucleus and umbra contracting at the same time. 5. The exterior boundary 

 of the umbra never consists of sharp angles, but is always curvilinear, how irre- 

 gular soever the outline of the nucleus may be. 6. The nucleus of a spot, while 

 on the decrease, in many cases changes its figure, by the umbra encroaching 

 irregularly on it ; insomuch that, in a small space of time, new encroachments 

 are discernible, by which the boundary, between the nucleus and umbra, is per- 

 petually varying. 7- It often happens, by these encroachments, that the nucleus 

 of a spot is divided into 1 or more nuclei. 8. The nuclei of spots vanish sooner 

 than the umbrae. Many instances of this sort are to be seen in Hevelius' plates, 

 and the same is affirmed by Mr. Derham in the Phil. Trans. 9. Small umbrae 

 are frequently seen without nuclei. 10. An umbra of any considerable size is 

 seldom seen without a nucleus in the middle of it. 11. When a spot, which 

 consisted of a nucleus and umbra, is about to disappear, if it is not succeeded by 

 a facula; or more fulgid appearance; the place which it occupied is soon after 



