Maech,26, 1897.]- 



SCIENCE. 



497 



much more powerful means of driving than 

 any method we had heretofore tried. An 

 exposure of one second gives an excellent 

 negative of such common test objects as 

 coins in a purse, and an exposure of five 

 seconds is sufficient to give a negative 

 showing clearly all the bony structure of 

 the hand and wrist, a negative sufBcient 

 for the purposes of a surgeon. The best 

 negative of the hand is to be obtained in 

 about 20 seconds, and 45 seconds gives a 

 marked over-exposure. Not only the bones, 

 but the outlines of the cartilaginous and 

 fatty tissues, and the tendons, are shown in 

 a negative from a 25-seconds exposure. We 

 have not had any opportunity to take any 

 photographs through the body, but j udging 

 from results given by the flourscope this 

 method gives a far greater penetration of 

 the rays and a much sharper outline of the 

 shadows than any other we have used . The 

 fluorescence is absolutely steady ; the pul- 

 sations of the heart can be seen with start- 

 ling clearness, and the outline of the liver 

 and lungs may be sharply distinguished. 

 The details of the bony structure of the 

 trunk are also clearly shown. The ribs 

 appear as tubes rather than solid rods, ow- 

 ing perhaps to the outer portion being more 

 dense than the inner. The processes on 

 the spinal column are well marked. The 

 hand of the observer may be held between 

 the patient under examination and the 

 tube, and a clear image of its bones may be 

 seen even through the most dense portions 

 of the trunk. 



The tunstate of calcium crystals glow so 

 brightly as to make the screen have a dis- 

 tinctly granular appearance. Each crystal 

 seems to be separately illuminated like the 

 grains of sand on a piece of coarse sand 

 paper placed in the bright sunlight. 



The effect of prolonged running on the 

 tubes is very similar to that of a static ma- 

 chine, only more pronounced. The resist- 

 ance of a tube may be increased by running 



with closed spark-gap, making the concave 

 electrode cathode as usual. If the tube be 

 reversed the resistance will be lowered. It 

 is very often found that a tube which has 

 been run hard for some time when allowed 

 to cool will increase in resistance, so as to 

 be beyond the range of the coil. By run- 

 ning such a tube, making the concave elec- 

 trode anode on the coil a few minutes, the 

 resistance will be lowered. Slight warming 

 will facilitate matters. Again reversing the 

 tube and running with closed spark-gap, the 

 tube may be brought back to its maximum 

 efficiency in a very few minutes. We have 

 repeated this operation five or six times on 

 some of our tubes with good results. It is 

 needless to say that the above applies only 

 to focus tubes with a platinum anode. 



The part played by the spark-gap is not 

 yet clear to us, but we have noted the fol- 

 lowing observations : A spark-gap between 

 spheres is better than one between points. 

 Some tubes will run without a spark-gap, 

 but when the gap is used it should be on 

 the cathode end of the tube. The proper 

 adjustment of a spark-gap may increase the 

 intensity of radiation several hundred per 

 cent. 



The platinum anode in the focus tubes 

 which we use becomes red hot, and the 

 whole tube feels warm to the hand. This 

 is true of tubes which do not heat when 

 driven by a 12-plate, 26-inch Wimshurst 

 machine. 



As stated in our note of February 17th, 

 we are operating our induction coil by dis- 

 charging through its primary a condenser 

 which has previously been charged at 220 

 volts from the lighting mains. This 

 charging and discharging we now accom- 

 plish 250 times a second by means of a five- 

 part commutator on the shaft of a small 

 motor. Since the condenser is discon- 

 nected from the mains only when it has 

 risen to their voltage, there is no spark 

 ing when it is disconnected; and since 



