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Archives of an email list on the history of binoculars. - page 22 / 150

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eliminating fungus on, say, binocular optics.  The problem would be to determine the "therapeutic" dosage.

  Methacrylate is the chemical name of the precursor compound for a class of transparent plastic polymers -- to quote the Merriam Webster dictionary, "Polymethylmethacrylate (1936) is a thermoplastic resin of polymerized methyl methacrylate which is characterized by its optical clarity." and, "Methacrylonitrile, CH2:C(CH3)CN, Clear, colorless liquid boiling at 90 deg C; used to make solvent-resistant thermoplasic polymers and copolymers."  (See also similar entries for methacrylate ester and methacrylic acid).

  From the McGraw-Hill Dictionary of Scientific Terms:

  Polymethylmethacrylate -- thermoplastic polymer derived from methyl methacrylate, CH2==C(CH3)COOCH3; transparent solid with excellent optical qualities and water resistance; used for aircraft domes, lighting fixtures, optical instruments, and surgical appliances.  Sometimes abbreviated PMM, this is one of the earliest plastics used for lenses.  I believe "Plexiglas" is a Dupont trademark for similar transparent solid plastic compounds.  n-Butyl Methacrylate is evidently a clear liquid that would be polymerized (changed into the solid form) by the addition of some chemical agent and probably heat.  Some forms of modern optical cements contain the two chemicals (plastic precursor and polymerizing agent) in a liquid solution, and are activated (polymerized to form the solid) by exposure to heat or to Ultraviolet (UV) light.  This "hardening" action is different than for traditional Canadian balsam, which hardens by drying when heated, or evolution of the natural solvents.  Balsam also can deteriorate with exposure to heat, light, humidity, fungus, and age.  The modern plastic resins are designed and rigorously tested for superior resistance to all of these agents.

  I can't locate a reference that gives the refractive index for PMM just now.  It is somewhat lower than for glass.  The advantage in making complete lenses of thermoplastic resins is in volume production by molding the lenses, avoiding the grinding and polishing operations.  Plastic lenses are now very common in all kinds of inexpensive equipment. They are seldom used for precision lenses, partly due to the problem of poor scratch resistance.

  Of course, Peter's initial comment was concerning the use of the plastic in liquid form as a cement.

Gene Lucas      (17250)

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Subject: French vocabulary, unusual model from France

I wrote to list member Jean Laurent Pernice:

> Can I ask you a few questions about the meaning of French words?

> --Jumelle. This can mean prism binocular, or Galilean opera glass?

> --Is there another word for 'binoculars' in French? binoculaire?

> --Lunette d'approche. Does this mean a terrestrial, 'birding scope'  Can it mean 'rifle scope', to mount on a small gun?

> --Longues-vues Is this word still used? Does it mean hand held telescope?

> --Lunetiers:  There was a Societe des Lunetiers, Paris, maybe they made spectacles only

> Also, See the great pictures at:  http://histv2.free.fr/19/voir.htm

From: "jean-laurent.pernice" <jean-laurent.pernice@___o.fr>

Napoleon has been very frequently painted with  a observation monocular on his hand .

  The meaning of jumelle  is double in french.  first is twin the second is the same than binocular or binoculars (you can write and say one " jumelle "or one pair of "jumelles " .  This word is not specific for galilean or prismatic binoculars or opera glass , you can use " jumelle or jumelles " to speak about the 3 optics .

  The others words for  binoculars are " binoculaire " or "lunette binoculaire "

  The word binoculaire is use to describe the binoculars and also optic like microscope .

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