THE MAKING OF A BIG TELESCOPE

Lake County Press, Issue 982, 3 October 1901, Page 7

THE MAKING OF A BIG TELESCOPE

Why not build an immense telescope, and solve 'once for all the vexed questions of whether the moon is dead or whether there is life in Mars? Unfortunately this is not really a matter of money. The difficulty is in the making of the lenses. Those of the great Paris telescope are 49in in diameter. 9b wider than any yet made. Each v.etgbs 7001b, and cost Jtlo.OOO. Jo make such a lens is the most ticklish piece of work known to science. A single airbubble. even the thousandth part of an inch in diameter, will ruin the whole lens. The material has to be selected with the greatest ot care. It takes thirty hours to heat the glass oven, twenty-four more to fill it, thirty hours to melt the material into glass, fifteen hours more to stir it, tlie heat at first being so great that a man can only work for five minutes at a time. Then it has to cool for six weeks before the manufacturer can tell whether the operation is a success. If all goes well, be then has a block of glass suitable for making a lens out of. But three blocks out of five are, when cooled, found to be faulty. The lensmaker's troubles now begin in earnest. He Ims to cut or grind away all the imperfect parts of the gh\ss, and then heat it all over again, and mould it into a flat eight-sided plate. If in this second heating the temperature goes above l.SOOdeg the whole thing litis to be begun afresh. Then comes the polishing, first with coarse sand, then emery, then liner emery, going down grade bv grade till Ihe last polishing is done with rouge and the softest silk. There are only three men in the world who are capable of giving the final touches to a great telescopic lens. The work is done by eye and touch. Measuring instruments cannot be used for fear of scratching. And the glass must he kept at a dead-level temperature, for a few degrees would raise on its surface lumps and bumps, which, though so slight as to be invisible, might make a difference of five miles to the apparent height of the mountains in the moon. Alvan Clark, the greatest expert in the matter of lens-mak-ing, said before his recent death that a lens might be made sft across. More than that lie thought, with present methods, impossible. Such a telescope will cost the enterprising millionaire who builds it anything up to £150,000.