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Dr Jean Laby was interviewed in 2000 for the Interviews with Australian scientists series. By viewing the interviews in this series, or reading the transcripts and extracts, your students can begin to appreciate Australia's contribution to the growth of scientific knowledge.
The following summary of Laby's career sets the context for the extract chosen for these teachers notes. The extract covers how she studied cosmic rays with the use of high-altitude balloons. Use the focus questions that accompany the extract to promote discussion among your students.
Jean Laby was born in 1915 in Melbourne, Victoria. She received a BSc in 1939 an MSc in 1951 and PhD in 1959, all from the University of Melbourne.
Laby was employed by the University in 1940 to work in the Department of Natural Philosophy, later named the Physics Department. Serving initially as a part-time demonstrator she was appointed to the position of lecturer in 1959. Her research was in the area of cosmic rays and wind studies.
While continuing as a lecturer at the University of Melbourne, from 1961-80, Laby also held a position as senior lecturer at the RAAF Academy at Point Cook, Victoria. During this time her research included radar meteorology and balloon-borne cameras as well as cosmic radiation measurements.
From 1972-80 Laby was involved in the Climatic Impact Assessment Program. In collaboration with the University of Wyoming, she measured atmospheric aerosols, ozone and water vapour in the stratosphere.
What did you do next?
At that time Dr V D Hopper offered me the opportunity to work on the cosmic ray project which he was doing with a group of others. I knew him quite well, as he used to come and help my father with the revision of his book, tables of physical and chemical constants, and I used to help with that too. Even when we went on holidays my father sometimes didn’t stop work, and Vic and I used to help him then with the revision also.
How did you detect the cosmic rays?
We used nuclear emulsions, which were thick layers of photographic emulsion on a thin glass plate. They were exposed to cosmic radiation by sending them up into the atmosphere, using balloons because aeroplanes did not get quite high enough.
There were two different types of balloons: expandable neoprene, which was an artificial rubber, and non-expandable plastic ones, which were not commercially available. You could make those yourself but they needed an enormous room and were very difficult to deal with (you had to test that there were no leaks at the joins and so on) so we didn’t use them. We used neoprene on the whole.
How big were these balloons?
The neoprene ones were about 3 to 6 metres in diameter, but they got up to 10-plus metres in the atmosphere when they expanded. The plastic ones were a different order of magnitude altogether, with diameters of hundreds of metres, and had to be launched by quite different methods. It took a team of people with trucks, cranes and goodness knows what to get everything into position, and the use of an aerodrome runway for launch.
The balloons were filled with hydrogen to make them ascend and as they went up into the more rarefied atmosphere they expanded and ultimately got to a stage where they burst – and that was the end of the flight. Our group, working together, devised a valve at the neck to keep them from bursting. The valves consisted of a metal tube with a ping-pong ball in the top to form a seal, the bell was attached to the top of the balloon by a length of string just less than the bursting diameter. A soft spring held the ping-pong ball down until the string unwound from the outside of the tube; when it reached the set height, the string lifted the valve and let out some of the hydrogen; and the balloon then just went on at that constant level.
Because the balloons would remain at a level height and float like that for hours, they gave our plates a very long exposure to the cosmic rays. The plates had to be recovered and then they were developed. They produced black grains where the rays had been through the emulsion and you could determine their properties from these, examining them under a microscope. We could also compare the results at different altitudes, varying the height at which we wanted the level flights by adjusting the length of the string. The longer the string, the higher the balloon would go, so long as it remained under the bursting diameter.
I understand that by 1952 your balloons reached above 24 kilometres and stayed there for about three hours, and by 1953 you got them up to 38 kilometres.
Yes. It was quite an achievement, I guess. In fact, the manufacturers of the balloons in America didn’t believe the heights we got. (I once saw how they used to predict the diameter at which the balloons would burst: it was done just by blowing them up gradually in an enormous room, to bursting point, measuring this size.)
Where did you launch the cosmic ray flights from?
Somewhere in Victoria, around Melbourne. For any of the balloon flights that were going to be in the air for a long time, the wind patterns would determine where you needed to launch them and where they were expected to end up. We needed somewhere good for recovery on landing – not in a forest or the sea. So on the day before a flight, we let a balloon off on its own, without any load, and then calculated what the winds were up to the required height, and forecast its trajectory.
After the pre-flight to forecast the wind, we had to prepare the balloon. That necessitated putting the valve in with the string and attaching it to the top of the balloon, before boiling the neoprene balloons (which performed better when they were boiled) and putting them in a plastic bag to take to the launch site the next day. Then we obtained from the weather bureau their forecasts as to where the skies would be clear of clouds so we could use our theodolites. Later on, the weather bureau were very cooperative and allowed us to use their radar at Laverton, which made it a much simpler operation, a different story altogether: there was only one place around Melbourne – the Laverton station – to operate for the tracking. That meant for tracking you were some distance from where the balloon was launched, and to find the balloon on the radar was sometimes difficult, particularly not knowing the exact time of release.
Select activities that are most appropriate for your lesson plan or add your own. You can also encourage students to identify key issues in the preceding extract and devise their own questions or topics for discussion.
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