Dr. Machta: I also have had opportunity for my say, so I'll be very brief. variability in space. As a synoptic meteorologist I recognize the For example, at our Helsinski meetings, very beautiful experiments using sodium vapor trails were reported on by the French. They fired sodium vapor trails up to about 80 to 120 kilometers and showed that at approximately 101 kilometers there was an abrupt transition between conduction and eddy mixing below, and apparently pure molecular mixing above. This is not quite the picture that one gets from what Ed (Martell) showed on the board here, indicating the variability in space. Down in Alice Springs they did this same experiment and got this transition at a completely different altitude. I really feel that taking one or two even very beautifully documented observations is not going to be the solution to our problem. Expensive though this may ultimately be, we are going to have to have many more of these. Dr. Shreve: I think there are some rather powerful ideas that are being thrown out here. Perhaps at the end they will come to the fore. Dr. Otting: As a means of thinking of related subjects I thought of what might be given at a symposium on upperatmosphere research rather than upper-atmosphere sampling. If you went to a meeting of this type, you could very well get into many things other than just particle sampling or static sampling. Certainly upper-air chemistry would be an important subject, as would the problems of radiation balance from the sun. things could affect the atmosphere generally. be very important and very difficult. In the region from 100, 000 to 500, 000 feet, air chemistry could There you run out of the simple methods of sampling, such as balloons, and you are in a region where you can't stay long in one place by any means. ficult region to study. All of these It is going to make it a very dif- On the other hand, electromagnetic techniques such as ionospheric studies and this sort of thing are already exploring this. As a matter of fact, one of our important problemsis the study of the D- region, which is in this part of the atmosphere. If the particles are in the charged state when you collect them, you undoubtedly are not going to have them in a charged state when you get them back to the laboratory, yet the electrical properties may be very important in their dynamics, even for general mass motions and this sort of thing. I don't have any proposal for a better sampling scheme, although Iam sure someof the people concerned with upper-atmosphere chemistry are concerned with this problem. particles from outside such as Captain Welch talked about. The same thing applies to the influx of These could complicate the situation by creating various kinds of electric and magnetic forces that would cause motions as you go further up. motions and things that could contribute information on particle motions or debris motion. We see mass I think there are other fields in the physical sciences exploring these areas, and these could very well contribute independent information on the subject that might be very useful. they knew enough about the other areas. I was interested in whether or not the people here felt that I know that Cambridge, for example, andI am sure the Weather Bureau and other places hear a lot about these things, and 1 wonder whether you should consider some of these things in your sampling and interrelate the information? 168