Reflection of Snow
Feb 14 07 – Akron, Ohio
It’s nasty out there. The snow is piling up and my co-workers are worried. They have raided the vending machine and have started stashing food in hiding places just in case we’re snowed in. I found one person on a chair, lifting ceiling tiles up checking for food stashes. He was hiding candy bars above the drop ceiling and wanted to make sure nobody else was doing the same. The wind driven snow is drifting across the door and the roads are report to be bad. No signs of cannibalism yet!
All that snow reminds be me of the incredible nature of water. Water decreases in density as we lower the temperature, but ice is one of the few solids which is less dense than its liquid phase. Thus ice floats. Good thing too! If ice was heavier than water the lakes and oceans would collect ice on their bottom. It doesn’t take too much imagination to realize that surface waters would slowly fill until the lakes and seas were frozen. Talk about changes in global weather, Earth would no longer be a blue ball as seen from space, but a dull white ball of ice.
If we go to Winchell’s “Optical Properties of Artificial Minerals” we find that ice has some interesting optical properties: Ice is a hexagonal system that is uniaxial positive. To optical crystallographers this screams that there are two refractive index and of the two, omega will always be detectable. The other value, epsilon, will show a projection value between zero and the true epsilon value. It also indicates there are three omega directions perpendicular to epsilon. The positive optical sign means the bigger of the two refractive indices will be the epsilon value. This is of value when attempting to determine the actual value from fragments without unique morphology related to optical axis like fibers.
In case you’re interested, the refractive indices of ice with yellow light are,
omega = 1.3091
and
epsilon = 1.3104.
The birefringence is the difference between omega and epsilon or 0.0013. This very small so don’t expect bright colors under crossed polars. The dispersion can be calculated from the refractive index values for blue, yellow and red light, but I leave that as an activity for the reader.
More interesting is the scientific description of precipated ice: “skeleton crystals very common in cold winters, often as basal tablets, hexagonal stars, dendrites…” Of course we know it as snow flakes.
Since I’m killing time while my co-workers draw straws to see who will attempt to go for help ( I work with a bunch of warm weather Texans, to whom snow and winter is total mystery) I am reminded at Wilson Bentley proved that no two snow flakes are identical. I’ve started reading his biography. In 1885 photography was still in its infancy, but Bentley was fascinated with drawing flakes. This was a time consuming activity and lacked some validity as a documentation process. Bentley invested in optical equipment and built a system, which would allow him to photograph single snowflakes. I’m sure you knew this, but what I find fascinating is that Bentley realized that alteration of his negatives would invalidate his studies. What Bentley would do was scrap the emulsion away so that only the flake of interest was present. Any distracting images would be removed with the emulsion. Bentley would first make a duplicate plate and keep the original plate in pristine condition. Any claim of fraud could be resolved by examining the original plate. He understood then what we and Photoshop are struggling with now: the alteration of images.
It’s nasty out there. The snow is piling up and my co-workers are worried. They have raided the vending machine and have started stashing food in hiding places just in case we’re snowed in. I found one person on a chair, lifting ceiling tiles up checking for food stashes. He was hiding candy bars above the drop ceiling and wanted to make sure nobody else was doing the same. The wind driven snow is drifting across the door and the roads are report to be bad. No signs of cannibalism yet!
All that snow reminds be me of the incredible nature of water. Water decreases in density as we lower the temperature, but ice is one of the few solids which is less dense than its liquid phase. Thus ice floats. Good thing too! If ice was heavier than water the lakes and oceans would collect ice on their bottom. It doesn’t take too much imagination to realize that surface waters would slowly fill until the lakes and seas were frozen. Talk about changes in global weather, Earth would no longer be a blue ball as seen from space, but a dull white ball of ice.
If we go to Winchell’s “Optical Properties of Artificial Minerals” we find that ice has some interesting optical properties: Ice is a hexagonal system that is uniaxial positive. To optical crystallographers this screams that there are two refractive index and of the two, omega will always be detectable. The other value, epsilon, will show a projection value between zero and the true epsilon value. It also indicates there are three omega directions perpendicular to epsilon. The positive optical sign means the bigger of the two refractive indices will be the epsilon value. This is of value when attempting to determine the actual value from fragments without unique morphology related to optical axis like fibers.
In case you’re interested, the refractive indices of ice with yellow light are,
omega = 1.3091
and
epsilon = 1.3104.
The birefringence is the difference between omega and epsilon or 0.0013. This very small so don’t expect bright colors under crossed polars. The dispersion can be calculated from the refractive index values for blue, yellow and red light, but I leave that as an activity for the reader.
More interesting is the scientific description of precipated ice: “skeleton crystals very common in cold winters, often as basal tablets, hexagonal stars, dendrites…” Of course we know it as snow flakes.
Since I’m killing time while my co-workers draw straws to see who will attempt to go for help ( I work with a bunch of warm weather Texans, to whom snow and winter is total mystery) I am reminded at Wilson Bentley proved that no two snow flakes are identical. I’ve started reading his biography. In 1885 photography was still in its infancy, but Bentley was fascinated with drawing flakes. This was a time consuming activity and lacked some validity as a documentation process. Bentley invested in optical equipment and built a system, which would allow him to photograph single snowflakes. I’m sure you knew this, but what I find fascinating is that Bentley realized that alteration of his negatives would invalidate his studies. What Bentley would do was scrap the emulsion away so that only the flake of interest was present. Any distracting images would be removed with the emulsion. Bentley would first make a duplicate plate and keep the original plate in pristine condition. Any claim of fraud could be resolved by examining the original plate. He understood then what we and Photoshop are struggling with now: the alteration of images.
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