I knew a valuable glass ruined by the proceedings of a workman who had been told to attach three pieces of brass round the cell of the double lens.

What he had done remained unknown, but ever after a wretched glare of light surrounded all objects of any brilliancy.
One word about the inversion of objects by the astronomical telescope.
It is singular that any difficulty should be felt about so simple a matter, yet I have seen in the writings of more than one distinguished astronomer, wholly incorrect views as to the nature of the inversion.
One tells us that to obtain the correct presentation from a picture taken with a telescope, the view should be inverted, held up to the light, and looked at from the back of the paper.

Another tells us to invert the picture and hold it opposite a looking-glass.

Neither method is correct.

The simple correction wanted is to hold the picture upside down--the same change which brings the top to the bottom brings the right to the left, _i.e._, fully corrects the inversion.
In the case, however, of a picture taken by an Herschelian reflector, the inversion not being complete, a different method must be adopted.