Haemacytometer and the like

Claim 1

A LIGHT TRANSMITTING OPTICAL DEVICE COMPRISING A TRANSPARENT SUPPORTING MEMBER FORMED OF A RELATIVELY HIGH SILICA BOROSILICATE TWO-PHASE TYPE OF GLASS HAVING A SILICA CONTENT OF BETWEEN APPROXIMATELY 70% AND 90%, A BORIC OXIDE CONTENT BETWEEN APPROXIMATELY 20% AND 6%, A SODIUM OXIDE CONTENT BETWEEN APPROXIMATELY 4.5% AND 2%, AND AN ALUMINUM OXIDE CONTENT BETWEEN APPROXIMATELY 6% AND 1%, SAID GLASS HAVING TWO PREDOMINANTLY DIFFERENT HEAT RESPONSIVE SOFTENING TEMPERATURE, SAID MEMBER HAVING A SMOOTH SURFACE THEREON, AND A SEMI-TRANSPARENT LAYER THEREON FORMED OF A METALLIC MATERIAL OF SUBSTANTIALLY UNIFORM DENSITY AND SELECTED FROM THE GROUP CONSISTING OF GOLD, SILVER AND THE PLATINUM METALS, AND HAVING A PLURALITY OF FINE SHARPLY DEFINED CLOSELY SPACED SUBSTANTIALLY PARALLEL RULED REFERENCE LINES THEREIN, ONE OF SAID REFERENCE LINES BEING SPACED FROM AN ADJACENT REFERENCE LINE BY AN AMOUNT APPROXIMATELY EQUAL TO FIVE HUNDREDTHS OF A MILLIMETER, SAID LAYER, BEING RELATIVELY HARED AND ABRASIVE RESISTANT AND TENACIOUSLY BONDED TO SAID SMOOTH SURFACE, AND HAVING THE CHARACTERISTICS OF A VACUUM DEPOSITED COATING, AND WITH THE BOND BETWEEN SAID LAYER AND SAID MEMBER HAVING CHARACTERISTIC LIKE THOSE RESULTING FROM THE HEATING OF SAID MEMBER AND SAID LAYER THEREON AT A TEMPERATURE BETWEEN THE LOWER OF SAID SOFTENING TEMPERTURES AND UPPER OF SAID SOFTENING TEMPERATURES FOR A TIME SUFFICIENT TO SOFTEN ONE OF THE PHASES OF SAID GLASS.