to be published before the end of the year.  Hariot had read some chapters; and saw that Gilbert defends the doctrine of a vacuum.  Not to leave a vacuum on this page (says Hariot), it is remarkable that though gold is both heavy and opaque, when beaten out into gold-leaf the light of a candle can be seen through it, though it appears of a green colour.

Letter 226, from John Kepler to Thomas Hariot, it
dated from

Prague, September, 1609.

Excuses himself for not having replied sooner; having been very busy; but would not lose the present opportunity of writing.  Discusses the questions of refraction and the vacuum.  Commentaries on Mars entitled ’Astronomia Nova [Greek Text] or Physica Cælestis,’ have been published at Frankfort; has not a copy by him.  Regrets to hear of the death of Gilbert.  Hopes his work on Magnetism will also be published; and that Erikson will bring a copy with him.  Promises to send a copy of his own meteorological observations; and hopes to receive Hariot’s.

These studies in optics and this correspondence with the learned Kepler indicate Hariot’s great advancement in natural philosophy as early as 1606 to 1609 and give an earnest of his inventive genius and scientific enterprise with his telescope in the astronomical discoveries which immediately followed in 1609 to 1613.  Before awarding all the prizes for discoveries and inventions in mathematics, philosophy and natural science to claimants throughout the wide Republic of Letters, let modest Hariot be heard and examined.  Let his papers and all his credentials be laid out before the high court of science, not in the light of today, but contemporaneously with those of Tycho, Kepler, Galileo, Snell, Vieta and Descartes.  Hariot himself has claimed nothing, but Justice and Historical Truth are bound to assign him a niche appropriate to his merits.

To show that Hariot, like his friends Hakluyt and Purchas, was alive to everything geographical as well as mathematical going on, the following is given from the original manuscript among the Hariot papers in the British Museum (Add. 6789): 

Three reasons to prove that there is a passage from
the North’ west into the South-sea.
1.  The tydes in Port Nelson (where Sr.  Tho :  Button did
winter, were constantly, 15, or, 18, foote ; wc is not found
in any Bay Throughout the world but in such seas as lie open
att both ends to the mayne Ocean.
2.  Every strong Westerne winde did bring into the Harbor where
he wintered, soe much water, that the Neap-tydes were equall
to the Spring-tydes, notwtstanding yt the harbor was open only
to ye E.N.E.
3.  In comming out of the harbor, shaping his course directly
North, about, 60, degrees, he found a stronge race of a tyde,
set-ting dueEast and West, wc in probabilitie could be noe
other thing, than the tyde comming from the West, and
retourning from the East,