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From Texereau's inspiration: metal marble:

interpretation   treatments

Work continues with emery 1m whose grains are comparable to those carbo 100 or 120 , but that leaves less deep fractures because of its lower hardness . Now we will adopt general way for the rest of the work, a normal stroke on which it must attract the attention specially: they consist a back and forth roughly centers (Fig 22 and 23), the total amplitude is about 1/3 of the disk diameters (therefore it is necessary to exceed one sixth of each side , 3 to 4 centimeters with a mirror of 20 centimeters), with a lateral departure constantly variable limit 1/8 at the each side.   the shape of the strokes may well affect that of a V or W or of a loop more complicated ∞ as an example ( G. W. Ritchey ) . Every five or six strokes it turns a little the upper disk in his hands and one turns oneself as in  roughing(coarse grinding) . What is essential in all this is only to respect roughly 1/3 the average amplitude and to vary as most p...

The gap of sphericity can exceed 2/10 of a millimeter on a mirror of 20 centimeters, it must be remembered has complete roughing by a slower method but catching this defect. It's not difficult, just keep working with racing roughly CENTERED as in Figure 18 B, but with a total range of motion not exceeding this time disk diameter of half

To deepen the mirror ( hogging out ) fastest way: the mirror of the center can go with safety until 1 or 2 centimeters edge of the tool and the straight runs being managed along chords may have ten centimeters with glasses of 20 centimeters diameter ; a little bit of experience indicate the non-hazardous limit for tilting the mirror on the edge of the tool. One can be five to ten straight races on site, then one rotates a fraction of turn the mirror in the hands and it resumes work in a direction slightly different , move around the post. If the post(stand) allows full rotation of the operator, the tool can remain stationary ; otherwise it is necessary to turn the timely manner a user also all its periphery. We see in Figure 18A, the figure described by the mirror of the center during this work

From cosmoquest In a Newtonian telescope, a parabolic mirror is usually used, since that surface focuses light from infinity to a nearly perfect on-axis image. Some telescope manufacturers (and a few amateurs) substitute longer f/ratio spherical mirrors, since they may sometimes be easier for some people to figure and test rapidly. However, if the f/ratio isn't long enough, the performance (especially at high power and for planetary viewing) may suffer. One way to rate telescope mirrors is by seeing how much their surfaces deviate from a perfect parabolic shape. One common rule of thumb states that the telescope's optics must not produce a wavefront error of more than 1/4 wave in order to prevent optical degradation. This requirement is sometimes extended somewhat to require that the mirror's surface must not deviate from a "perfect" paraboloid surface by more than an eighth wave (approximately 2.71 millionths of an inch) in order for the mirror ...

The mentality which is embodied by NBA legend Kobe Bryant and has defined his career and accolades. Kobe on the Mamba Mentality: ""If you see me in a fight with a bear, prey for the bear". Ive always loved that quote. Thats "mamba mentality" we don't quit, we don't cower, we don't run. We endure and conquer. Stop feeling sorry for yourself, find the silver lining and get to work with the same belief, same drive and same conviction as ever...Mamba Out."