Scientists working on a problem do not know and sometimes can't even guess what the final

result will be. Late on Friday, 8 November, 1895, Professor Rontgen, a German physicist, was doing an experiment in his laboratory when he noticed something extraordinary. He had covered an electric bulb with black cardboard, and when he switched on the current he saw little dancing lights on his table. (46) ; how then could any ray penetrate？ On the table there were some pieces of paper which had been covered with metal salts. (47) . Professor Rontgen took a piece of this paper and held it at a distance from the lamp. Between it and the lamp he placed a variety of objects, a books, a pack of cards, a piece of wood and a door key. The ray penetrated every one of them except the key. He called his wife into the laboratory and asked her to hold her hand between the lamp and a photographic plate. (48) , but she held up her hand for a quarter of an hour, and when the plate was developed there was a picture of the bones of her hand and of the ring on one finger. The mysterious ray could pass through the flesh and not through the bone or the ring.

At a scientific meeting, Professor Rontegen called this new ray "the unknown", the X-ray. (49) , and soon there were X-ray machines in all the big hospitals. The most obvious use for this discovery was to enable doctors to see exactly how a bone was fractured. Other uses came later. It was found that these rays could be used to destroy cancer cells, just as they destroyed the healthy cells of the doctors who first used the machines. (50) , and the lungs could be X-rayed to show if there was any tuberculosis present.

A. It was on this paper that the lights were shining

B. She was very surprised by this request

C. Now the bulb was completely covered

D. It was a great invention

E. Methods were found later by which ulcers in the stomach could be located

F. Doctors quickly saw how this could be used

(46)