344 



A' A TURE 



iFeb. lo, 1 88 1 



detached or melting, notwithstanding the temperature 

 was so high that the paper scale at that portion of the 

 stem to which the ice ching was charred ; this was the 

 case in one of the experiments shown at the Chemical 

 Society. In another instance I have had a thin circular 

 piece of ice attached to the otherwise bare bulb of the 

 thermometer, and though this piece was very thin and no 

 more than about 2 mm. diam,, it took fully one minute or 

 more to volatilise, notwithstanding the thermometer indi- 

 cated a mean temperature of about 70° C, and the sur- 

 rounding tube was very hot. If the ice were not capable 

 of being heated above its melting-point, a piece so small as 

 that referred to would, I think, under these circumstances 

 have fused or volatilised almost instantaneously. If the ice 

 be really above 80° C. it ought to melt suddenly and at once 

 on discontinuing the heat and increasing the pressure, and 

 this I have in one or two instances found to be the case. 

 Thus in one experiment a beautiful rod of ice nearly six 

 inches long and about half an inch diameter was attached 

 to a glass rod suspended in the apparatus described above 

 and heated very strongly with a large Bunsen's burner for 

 several minutes ; the pressure was then let in, when the 

 ice at once fell off the rod into the mercury trough below, 

 melting completely, and as far as could be seen even 

 before it reached the mercury. Careful observations have 

 also been made to see whether any cavity could be 

 detected between the ice and the hot thermometer when 

 the latter was only partially covered with ice, and indi- 

 cated a high temperature, but such could not be seen 

 either with ice or mercuric chloride. In both cases the 

 substance appeared to rest in actual contact with the 

 bulb of the thermometer, in this respect differing from 

 camphor, which does exhibit such a space. I have how- 

 ever never been able to get camphor above its ordinary 

 melting-point, though by reducing the pressure below 400 

 mm., it solidifies while boiling, and cannot be re-melted 

 unless the pressure be increased. 



One curious point about the ice experiments is the 

 comparative slowness with which the ice appears to 

 evaporate, though the surrounding tube is very strongly 

 heated. 



In conclusion, I need hardly say that it is highly desir- 

 able that my results should be confirmed by other 

 observers. Thos. Carnelley 



TELE-PHOTOGRAPHY 



VA/'HILEexperimenting with the photophone it occurred 

 '' * to me that the fact that the resistance of crystalline 

 selenium varies with the intensity of the light falling upon 

 it might be applied in the construction of an instrument 

 for the electrical transmission of pictures of natural 

 objects in the manner to be described in this paper. 



In order to ascertain whether my ideas could be carried 

 out in practice, I undertook a series of experiments, and 

 these were attended with so much success that although 

 the pictures hitherto actually transmitted are of a very 

 rudimentary character, I think there can be little doubt 

 that if it were worth while to go to further expense and 

 trouble in elaborating the apparatus excellent results 

 might be obtained. 



The nature of the process may be gathered from the 

 following account of my first experiment. To the nega- 

 tive (zinc) pole of a battery \vas connected a flat sheet of 

 brass, and to the positive pole a piece of stout platinum 

 wire ; a galvanometer was interposed between the battery 

 and the brass, and a set of resistance-coils between the 

 battery and the platinum-wire (see Fig. I, where r, is the 

 battery, R the resistance, P the wire, M the brass plate, 

 and G the galvanometer). A sheet of paper which had 

 been soaked in a solution of potassium iodide was laid 

 upon the brass, and one end of the platinum wire pre- 

 viously ground to a blunt point was drawn over its sur- 

 face. The path of the point across the paper was marked 



by a brown line, due, of course, to the liberation of iodine 

 When the resistance was made small this line was dark and 

 heavy; when the resistance was great the line was faint 

 and fine ; and when the circuit was broken the point made 

 no mark at all. If we drew a series of these brown lines 

 parallel to one another, and very close together, it is 

 evident that by regulating their intensity and introducing 

 gaps in the proper places any design or picture might be 



represented. This is the system adopted in Bakewell's well- 

 known copying telegraph. To ascertain if the intensity of 

 the lines could be variedby the actionof light, 1 usedasecond 

 battery and one of my selenium cells, made as described 

 in Nature, vol. xxiii. p. 58. These were arranged as 

 shown in Fig. I, the negati7'e pole of the second battery, 

 b', being connected through the selenium cell S with the 

 platinum wire P, and the positive pole with the galvano- 

 meter G. The platinum point being pressed firmly upon 



the sensitised paper and the selenium exposed to a strong 

 light, the resistance R was varied until the galvanometer 

 needle came to rest at zero. If the two batteries were 

 similar this would occur when the resistance of R was 

 made about equal to that of the selenium cell in the light. 

 The point now made no mark when drawn over the paper. 

 The selenium cell was then darkened, and the point 

 immediately traced a strong brown line ; a feeble light 

 was next thrown upon the selenium, and the intensity of 



