lie 5 8 
NovEMBER Ig, 1896] 
NATURE 65 
passing through the whole three to give a shadow of the bones 
of the hand on another screen. I have advantageously em- 
ployed a large screen, therefore, in which the crystals are even 
coarser than those previously used, and the thickness very much 
increased. By this means I have now no difficulty in seeing 
many of the deep structures of the body in movement. 
Different Conditions of the Tube may be utilised for Different 
Lffects. 
Lately I have been trying to follow up Prof. J. J. Thomson’s 
suggestion about there being different kinds of X-rays, in order 
to discover, if possible, whether a particular set of rays might be 
utilised for different tissues. Whether it bea matter of difference 
or intensity or difference in quality (as Prof. Thomson suggests), 
there can be no doubt with the tube in a certain condition 
the bones of the hand appear jet black on the fluorescent screen, 
while the soft tissues are scarcely visible. On the other hand, 
in a different condition of the tube the soft tissues are much 
more prominent and the bones faint. Following up this inquiry, 
I made a series of experiments by way of placing metal rings 
near the kathode, some of them earthed and all adjustable. I 
am quite aware others have placed rings of metal near the kathode, 
and described alterations in the tube which they have attributed 
to different causes. The sole object in my experiments was to 
afford an indication of alteration in a given condition of the tube. 
These experiments were so far successful, but I found much the 
same results could be obtained by using the discharge rods of the 
coil. The method adopted was, first, to heat the tube by means 
of a Bunsen burner until I got the exact condition required. 
The discharge rods were approximated until they cut out the 
focus tube, and then one was very slightly withdrawn until the 
tube again became fluorescent. The slightest alteration in the 
vacuum afterwards was immediately indicated by sparking across 
the gap. It need hardly be pointed out thatan arrangement like 
Mr. Campbell Swinton’s for correcting the vacuum by means of 
a magnet instead of heat would be an advantage if it could be 
applied to the ordinary focus tube. Once having selected the par- 
ticular condition required, a small Bunsen burner below the tube 
may be so regulated as to give the necessary heat. By these 
means a particular condition of the tube may be kept up for a 
very long period without trouble. I have had it going on 
constantly in some instances for half-an-hour at a time with 
little or no apparent change in the appearance of the shadow 
of the tissues, and consequently had no difficulty in focusing 
the fluorescent sereen on the ground glass of the camera, nor in 
photographing the sereen with shadows of objects thereon. 
Action upon Tissues and Fluorescent Screens. 
Actions upon the tissues of the body have been recorded from 
several sources, and severe loss of skin and hair asa direct result 
of the application of the rays has been noted. Although I worked | 
for months, it was only within the last few weeks that, having 
to place my hand near the tube, between it and the fluorescent 
screen, for long periods and several nights in succession, evidence* 
of a dermatitis ensued. The hand looked as if it had been sun- 
burned, and became red and swollen; there was afterwards 
shedding of epidermis and loss of hair. The severer effects re- 
mained for over a fortnight. 
Another curious action on the tissues was noticed while photo- 
graphing a fish. The apparatus used was the old form of German 
tube, and an induction coil with Tesla. After half-an-hour’s 
exposure the back of the fish was covered with patches of phos- 
phorescence, which remained for some hours afterwards. 
It is usually considered that the action of the rays upon the 
potassium or barium screen is of very short duration. I have 
several times tried to see if the luminescence remained for any 
length of time after the current had been turned off, but could 
never record anything definite in this way. For redsons which 
need not be here entered upon, I had been experimenting with 
a view of putting the fluorescent screen into a particular con- 
dition for a period of time, and some metal objects were hung 
over the back of the screen to serve as a shadow. It was ex- 
posed to the effects of the rays for a quarter of an hour, and 
afterwards set aside where it was not acted upon by the day- 
light. The following evening I resumed my experiments, and 
found an image of the metal ring which had been used the 
previous night. The bluish colour was different inside and out- 
side of the ring from that part of the screen which had been 
protected by the metal. The screen was immediately put past 
and examined for four nights in succession ; each time, though 
NO. 1412, VOL. 55] 
less distinct, I could see the image, and it did not completely 
disappear for a week, during which time the screen was kept in 
the dark. 
With regard to the action upon the tissues, I think it right to 
point out that there are at least two other forces at work—heat 
and electricity—and that while the former might not have much 
to do with the action on the skin, the latter might. In any case, 
however, the above-mentioned results were obtained after, and 
seem to have been the direct result of exposure to the action of 
forces in the region of the focus tube. 
JOHN MACINTYRE. 
JUMPING COCOONS. 
‘THE curious movements of jumping beans have lately at- 
tracted some attention, though to style the spasmodic jerks 
of the beans jumps is to court disappointment. Some ‘‘ jumping 
cocoons,” described by Dr. D. Sharp in the Ex/omologést, were 
however, remarkably good athletes, for they could spring out of 
a small vessel, such as a tumbler, in which they were placed. 
These cocoons were from South Africa, but in spite of their 
exceptional gymnastic efficiency, Dr. Sharp hardened his heart and 
sacrificed them upon the altar of science, in the hope of dis- 
covering something unusual that would explain the powers of 
jumping. The cocoons looked like a piece of oval pottery, 
about five millimetres long, and having a rough surface. In 
each of the two investigated a pupa was found; the two were 
similar in every respect, and they no doubt belonged to the 
larvee that made the cocoons. ‘‘ This little pupa,” says Dr. Sharp, 
““is shut up in a remarkably hard thick cocoon, and it has to get 
out. Nature has not provided it with caustic potash for the 
purpose, but has endowed it with a mechanism of complex 
perfection to accomplish this little object. On the front of the 
head it has a sharp chisel edge, and with this it has to cut through 
the pottery ; contracting itself to the utmost in the posterior part of 
the cocoon, and retaining itself in this position by the hooks on 
the mobile part of the body, it is in a condition of elastic tension 
in consequence of the other side of the body being so differently 
formed and immobile ; therefore, releasing the hold of the hooks, 
the pupa is discharged forwards, and the chisel piece strikes the 
front part of the cocoon ; repeating this an enormous number 
of times a circle may be gradually inscribed on the inside 
of the far end of the cocoon, which gives way when 
sufficiently weakened, and the insect becomes free. In both 
the specimens the inside of the cocoon is about half-cut 
through; either this is done as the result of a prolonged 
series of wriggles, or of shocks such as I have described. 
It is by no means improbable that the early part of the 
performance is carving the groove by wriggling, the later 
part knocking it off by jumping against it.” The pupa is 
thus a most interesting one to entomologists. The order of 
insects to which it belongs appears to be somewhat uncertain, 
but Dr. Sharp thinks it will prove to be an anomalous lepid- 
opterous insect allied to Trichoptera, and possibly somewhere 
near to Ade/a. 
MECHANICAL CONCEPTIONS OF 
ELECTRICAL. PHENOMENA. 
MATTER AND MOTION. 
JNTIL the middle of the present century the reigning 
physical philosophy held to the existence of what were 
called imponderables. The phenomena of heat were explained 
as due to an imponderable substance called ‘‘ caloric,” which 
ordinary matter could absorb and emit. A hot body was one 
which had absorbed an imponderable substance. It was, there- 
fore, no heavier than before, but it possessed ability to do work 
proportional to the amount absorbed. Carnot’s ideal engine 
was described by him in terms that imply the materiality of 
heat. Light was another imponderable substance maintained 
by Sir David Brewster as long as he lived. Electricity and 
magnetism were imponderable fluids, which, when allied with 
ordinary matter, endowed the latter with their peculiar qualities. 
During the fifty years, from about 1820 to 1870, a somewhat 
different kind of explanation of physical events grew up. The 
1 Abridged from a lecture delivered before the Franklin Institute by 
Prof. A. E. Dolbear. 
