chart of "Reflection from the Ionosphere" from Feb 1933 to June 1934
Date: 1934
Inventory Number: 1998-1-1434
Classification: Chart
Dimensions:151 x 55.7 cm (59 7/16 x 21 15/16 in.)
folder: 0.5 x 92 x 61.5 cm (3/16 x 36 1/4 x 24 3/16 in.)
DescriptionSix line graphs plotting various factors in measuring reflection from the ionosphere. The axis is numbered six times with different scales. The graph on the bottom is numbered from 0 to 50; the next one up is labeled 0, 1, 2, with all values circled. The "2" coincides with the next scale, which is numbered 0 to 400. The next one up is labeled 0 to 50. The one after that is labeled "hours after sunrise" and labeled from -1.5 to 1.5. The next graph is labeled "hours after sunset" and numbered from 7 to 0. The horizontal axis is labeled with the date, which spanned February 1933 to June 1934.
The graph on the bottom is in green and starts off the chart in the territory of the next graph. It has periods of flatness at zero with occasional maxima. The two highest points are in February of 1933 and May 1934. A smooth curve is drawn in red through the graph.
The next graph up has lines in gray and red and is labeled in faint pencil. The inscription most likely reads "Mag. clar. of day." The gray line is characterized by plateaus, while the red line tends to fluctuate more. Points are occasionally marked "storm" in gray.
The next graph up has lines in gray and red. It begins at a sustained zero until taking off, rising, and then coming down to zero again. The gray line marks the fluctuations, while the red marks the general trend.
The next two graphs are each the hours of the day. They each have gray and red lines. The gray lines are in pairs, with one connecting the plots and charting the fluctuations, while the other is smooth and charts the trend. The same is true of the red lines. The lines break into dotted lines when the line drops into the area of the other graph. A note at the top says that two hours of the morning is equal in scale to six hours in the evening.
Inscribedtop (upside down): STANDARD CROSS SECTION 10 X 10 / KEUFFEL 7 ESSER CO - NEW YORK MADE IN U.S.A. [repeats three more times]
top (handwritten): 2 hours AM = 6 hrs. pm
along vertical axis, bottom to top: 0 / 10 / 20 / 30 / 40 Mag. C[lar?] of Day 0 / 1 / 2 0 / 100 / 200 / 300 0 / 25 / 50 HOURS AFTER SUNRISE -1.5 / -1.0 / -0.5 / 0 / 0.5 / 1.0 / 1.5 / 2.0 / 2.5 HOURS AFTER SUNSET 7 / 6 / 5 / 4 / 3 / 2 / 1 / 0
written on back: Chart dated 1933-34 / "Reflection from the Ionosphere" / Ionization layer in Atmosphere 1J-1j / 1998-1-1434
FunctionThe ionosphere is the section of the upper atmosphere, mostly the thermosphere and exosphere, in which enough particles are ionized by ultraviolet and X-rays from the sun that they interfere with radio wave transmission. The reflection of an ionospheric layer depends on its density of ionized particles and the frequency of the waves. The greater the density, the higher the frequency that can be reflected. The uppermost frequency to be reflected is known as the critical frequency.
Because many of the vertical axes are unlabeled on this sheet, it is difficult to tell exactly what is being charted. However, it is likely that it is charting the height at which the ionosphere reflects a particular frequency of radio waves.
ProvenanceBlue Hill Meteorological Observatory?
Although there is no signature of the Blue Hill Observatory, the observatory did conduct observations on signal propagation from its 5m radio transmitter in the early 1930s, so it is possible that these observations were part of this project (see Related Works).