Another experiment consisted in placing the radium against the bone at the side of the forehead, and even in this position, with the eyes closed, a light was perceptible, although fainter. Here the radium rays had acted upon the eyeball through the bones of the head. "It is possible," said M. Curie, "that this property of radium may be utilized in certain diseases of the eye. Dr. Emile Javal, one of our distinguished physicians, who is blind himself, has given this matter particular attention, and he thinks that radium may offer a precious means of diagnosis in cases of cataract, by showing whether the retina is or is not intact, and whether an operation will succeed. If a person blind from cataract can see the radium light as you have just seen it, then the eyesight of that person may be restored by removing the cataract. Otherwise it cannot be restored." As we returned to the laboratory I remarked that the quantity of radium in the various tubes I had seen was very small. "Of course it is small," he sighed; "there is very little radium in the world. I mean very little that has been taken from the earth and purified." "How much is there?" He thought a moment. "We have about one gramme (one-third of an ounce) in France, Germany may have one gramme, America has less than one gramme, and the rest of the world may perhaps have half a gramme. Four grammes in all would be an outside estimate; you could heap it all in a tablespoon." I suggested to M. Curie the possibility that some philanthropist might be inspired on reading his words to help the new cause. And I remarked that great things could doubtless be accomplished with some substantial quantity of radium, say a pound or two. He gave me an amused look and asked if I had any idea what a pound or two of radium, say a kilogramme (two and one-fifth pounds), would cost. "Why, no," said I, "no exact idea; but----" "A kilogramme of radium would cost"--he figured rapidly on a sheet of paper--"with the very cheapest methods that we have of purifying the crude material it would cost about ten million francs (£400,000). Under existing conditions radium is worth about three thousand times its weight in pure gold." "And yet there may be tons of it in the earth?" M. Curie was not so sure of this. "It is doubtful," said he, "if there is very much radium in the earth, and what there is is so thinly scattered in the surrounding ore--mere traces of radium for tons of worthless rock--that the cost of extracting it is almost prohibitive. You will realize this when you visit our works at Ivry."