BENEDICTUS SPINOZA
   Baruch Spinoza (1632-1677), of Amsterdam and Voorburg, Holland, from a 
Portuguese family, was a Jewish philosopher who was expelled from the 
religious community and afterward took the Latin name Benedictus.  His 
chosen occupation was lens grinding, a craft exercised by scientists and 
the educated persons of his era.   Holland was the center of this business, 
and as a new trade, it was not governed by a guild and was open to those of 
varied backgrounds.
   Telescopes and microscopes were produced & signed by Spinoza; though it 
is possible that he made only the optics.  Herzog Ernst I, von Sachsen-
Gotha (Duke Ernst I, 17th century), owned a very large collection of 
telescopes, including examples by Spinoza, which survive as of 2001.
   Spinoza wrote and read extensively on practical and theoretical optics.  
There are many letters from the era that describe Spinoza fabricating 
telescopes and microscopes that were praised by scientists, including 
Leibniz and Christiaan Huygens (with whom Spinoza observed Jupiter, using 
Huygens' 30 foot telescope).  Spinoza's letters describe his observations 
of blood and of insects using a microscope.  His works included 'Treatise 
on the Rainbow', published anonymously in Dutch in 1687; then lost until it 
was discovered & reprinted in 1862.  However, his writings on theoretical 
optics are not on a par with his correspondents, some of the leading 
scientists of his day.

   Spinoza has 'taken his special exercise in the optics and in the 
grinding of magnifying glasses and telescopes'.  -Jarig Jelles, a 
correspondent of Spinoza's, in a biographical essay.
   'The Jew of Voorburg finished his small lenses by tool. The results were 
quite remarkable'  -Christiaan Huygens.
   Spinoza 'so well succeeded that People came to him from all Parts to buy 
his glasses; which did sufficiently afford him wherewith to live and 
maintain himself.'  -Johannes Colerus, 1705 biography.
   'He supported himself by his work of making all kinds of lenses for 
optical use, according to mathematical formulae'.  -Balthasar Bekker, 1691.

   Spinoza did not use machines but relied on very time consuming hand 
work, producing quantities of glass dust, which is very damaging to the 
lungs.  He worked at lens making to his demise, dying in 1677 at 44 years 
of age, of consumption aggravated by glass particles.  Lenses found in 
Spinoza's shop after his death were sold for high prices.

   Extensive correspondence to & from Spinoza has been published.  Excerpts 
follow:

   Spinoza, letter to Henry Oldenburg of the Royal Society in London, 20 
November 1665, Wolf p213: 'The said Huygens was, and is still, fully 
occupied in polishing dioptrical glasses.  For this purpose he has 
constructed a machine, in which he can turn tools, and it is indeed 
sufficiently neat.  But I do not yet know what advance he has made thereby, 
nor, to confess the truth, do I greatly desire to know.  For experience has 
taught me sufficiently that in spherical tools it is safer and better for 
glasses to be polished with a free hand than by any machine.'
   Oldenburg, reply to preceding, Wolf p215: '….communicating to me also 
anything you may have learnt about the success of Huygens in the polishing 
of Telescopic Glasses.'   (Christiaan Huygens was very secretive, writing 
to his brother Constantyn to say that no information should be given to 
Spinoza and that all possible information should be obtained from Spinoza, 
who was frequently discussed by the brothers.)
   Spinoza to Oldenburg, 1665, wrote that new telescopes from Italy had 
been used to observe rings of Saturn, and shadow transits on Jupiter.

   Johannes Hudde was a mathematician, scientist, & lens grinder of 
Amsterdam, the author of 'Dioptrics' (of which there is no extant copy).  
Spinoza used Dioptrics to calculate & determine that, in a telescope, 
plano-convex lenses are superior to concavo-convex lenses.  Spinoza  wrote 
a letter to Hudde that described the infinite divine nature & then followed 
with a formula for calculating the shape of grinding tools for lenses.
   Spinoza to Hudde, June 1666, Wolf p225: 'I have a mind to get new tools 
made for me for polishing glasses....I do not see what advantage we obtain 
by polishing convex-concave glasses.  On the contrary, convex-plane lenses 
must be more useful, if I have made the calculation 
correctly....(calculations)....the reason why convex-concave glasses are 
less satisfactory is that, besides requiring double the labour and expense, 
the rays, since they are not all directed towards one and the same point, 
never fall perpendicularly on the concave surface.'

   Spinoza to Jarig Jelles, 03 March 1667, Wolf p231:  '....if nothing else 
is taken into consideration except the length of the eye or of the 
telescope, we should be obliged to make very long telescopes before we 
could see the objects on the Moon as distinctly as the objects which we 
have here on earth.  But, as I have said, it turns chiefly on the size of 
the angle which is formed by the rays coming from different points, at the 
surface of the eye, when they cross each other there.  And this angle also 
becomes greater or less according as the foci of the glasses put in the 
telescope are more or less distant.'

   Letter from Gottfried Leibniz, 05 October, 1671, Wolf p261: 'Among the 
other praises of you which fame has bruited abroad, I understand is your 
great skill in optics....This paper which I send you....'A Note on Advanced 
Optics'....sufficiently explains its object......the 'Prodomus' of Francis 
Lana, a Jesuit, a work written in Italian....makes some notable remarks on 
Dioptrics.  But Johannes Oltius, a young Swiss, very learned in these 
matters, has also published 'Physico-Mechanical Reflections on Vision', in 
which he promises some kind of very simple and universal machine for 
polishing all kinds of glasses'.
   Reply to preceding, Spinoza to Leibniz, 09 November, 1671, Wolf p263: 'I 
ask whether those lenses which you call 'pandochal' correct this error, 
that is, whether the Mechanical point, or the small space, in which the 
rays coming from the same point are collected after refraction, remains the 
same in size, whether the aperture is great or small?  For if the lenses 
achieve this, it will be possible to enlarge their aperture as much as one 
likes, and they will, therefore be far superior to those of any other 
shapes known to me; otherwise I do not see why you commend them so much 
more than the ordinary lenses.  For circular lenses have everywhere the 
same axis, and therefore, when we employ them, all the points of an object 
must be considered as if placed in the optic axis......when we wish to 
apprehend several objects in one glance (as happens when we employ very 
large convex eye-lenses), your lenses can be of help to represent the whole 
ensemble of things more distinctly.'
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References.  (Most of the published research on Spinoza makes no mention of 
his occupation.  Browne and Kayser, below, are journalistic and less than 
scholarly but are two of the very few works to confirm the subject of lens 
grinding.)

Browne, Lewis.  Blessed Spinoza.  N.Y.: Macmillan, 1932.

Gabbey, Alan.  Spinoza's natural science and methodology.  In: Garrett, 
Don.  The Cambridge Companion to Spinoza.  Cambridge: C.U.P., 1996.  
(pp150-154)

Kayser, Rudolf.  Spinoza: Portrait of a Spiritual Hero.  N.Y.: 
Philosophical Library, 1946.

Klever, W.N.A.   Spinoza's life and works.  In: Garrett, Don.  The 
Cambridge Companion to Spinoza.  Cambridge: C.U.P., 1996.  (pp150-154)

Pringle-Pattison, Andrew.  Spinoza.  Encyclopedia Britannica, 11th edition.  
Cambridge: E.B., 1911.

Wolf, A., translator & editor.  Correspondence of Spinoza.  N.Y.: Dial 
Press, 1927.
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