APRIL 12, 1901.] 
but this is just the opposite of the result 
of the eclipse observations. Furthermore, 
Plate III., ‘Pressure in Eclipses,’ shows us 
the variations in pressure as observed, and 
these are reproduced in the lowest section of 
the adjacent diagram. It is seen that the pres- 
sure in the eclipse is reversed throughout its 
length to that required in the cold-center cyclone. 
The Weather Bureau observations at sixty-five 
stations confirm the Clayton distribution of 
pressure, but the conclusion is also unavoid- 
able that we are not dealing with a cold-center 
cyclonic circulation. My further remarks on 
this subject will be found in the forthcoming 
report by the Weather Bureau. 
3. The Semidiurnal Cyclones.—Even if the 
analogue between the eclipse circulation and 
that assumed to exist in the nocturnal circula- 
tion were not hopelessly in error, there are yet 
other difficulties to be considered, even suppos- 
ing the cooled hemisphere of the atmosphere 
were to produce something like a cold-center 
cyclone and the heated hemisphere a warm- 
center cyclone. (a) The vertical circulation in 
the cold-center and in the warm-center cyclones 
are in opposite directions to one another at the 
belt of highest pressure, so that they would 
tend to destroy each other, rather than build 
up any high pressure belt such as the diurnal 
pressures require. (6) If there is a cyclonic 
circulation of any kind, the conditions demand 
that the pressure be distributed quite symmet- 
rically on all sides of the center in order to 
maintain a true gyratory motion; but in the 
diurnal barometric pressure there are found to be 
simply two peculiar waves extending from pole 
to pole, which do not in the least form such a 
symmetrically distributed pressure about a cen- 
ter. Compare Int’] Cloud Report, Chart 44. 
(ec) According to Clayton, Plate IV., the high 
pressures at the surface shift about 90° in the 
higher strata. But so far as I know, the only 
data bearing upon this point are contained in 
the Blue Hill hourly cloud observations, and 
these show that the same diurnal circulation ex- 
ists in the atmosphere from the surface to the 
cirrus level. However, this may be a doubtful 
point and I will not press its accuracy. Com- 
pare Int’] Cloud Report, Chart 45. 
I have generally found myself in accord with 
SCIENCE. 
591 
Mr. Clayton’s published results, and Iam sorry 
to be obliged to dissent from his interpretation 
of the eclipse observations in this case. The 
variations of pressure in the eclipse are not 
larger than 0.01 inch of mercury, and the 
velocity of the eclipse wind is only 2 or 3 miles ; 
but it would seem hardly credible in the face 
of these facts that this small atmospheric dis- 
turbance should set up any true cyclonic 
circulation over an area 5,000 miles in ex- 
tent, as is claimed in the report under consid- 
eration. 
FRANK H. BIGELOW. 
WASHINGTON, D. C., March 20, 1901. 
THE REVERSAL OF THE PHOTOGRAPHIC IMAGE 
BY CONTINUED ACTION OF LIGHT. 
THE remarkable results described by Professor 
Francis E. Nipher, in developing photographic 
plates in daylight, bring to mind some of the 
earlier experiments upon the reversal of the 
photographic image. It has long been known 
that under particular conditions of over-expos- 
ure in the camera a positive, instead of a nega- 
tive, is produced by ordinary development. 
This result has been repeatedly observed by 
amateurs, much to their astonishment and mysti- 
fication. 
The present writer has several times at- 
tempted to bring about the effect by prolonged 
exposure in the camera, but without success. 
The necessary conditions not being known, the 
result is accidental and uncertain. The idea of 
giving a supplementary exposure of the plate 
in broad daylight did not suggest itself; in- 
deed, itis not one that would spontaneously 
commend itself to a photographer. All his 
previous training and experience is opposed to 
it on general principles. 
Nevertheless, it is not entirely new. Her- 
schell, in the year 1839 or 1840, did very much 
the same thing. He observed reversals of 
photographic action, and so did Draper on strips 
of sensitized paper with which he was studying 
the chemical action of the sun’s light in Vir- 
ginia, and photographing the spectrum in 
ephemeral colors. This subject was referred to 
quite recently in an article by the present 
writer, entitled, ‘Tithonic Rays and Early 
