The terms “ Flying—boat ” and “ Seaplane ” convey to our minds two distinct types of marine aircraft, which have many points in common and yet many points not in common, and together they cover such a vast amount of subject matter,that it is only possible to deal with a limited number of aspects in this paper.

As the subject of the reduction of astronomical observations in the air had been the subject of several conversations with the late Squadron Leader Johnston, who was one of our best exponents of aerial navigation, Mr. A. J. Hughes, O.B.E., suggested to the writer that a short note based on Squadron Leader Johnston's methods would be useful in order that his valuable experience should not be entirely lost, and that some systematic survey of the methods available would be useful in connection with a subject that is becoming of increasing importance now that the range and reliability of aircraft have been so largely extended.

Petroleum as it occurs in Nature is a very complex mixture of hydrocarbons. Imagine a mixture of petrol, paraffin, gas oil, fuel oil and lubricating oil, together with a certain amount of water and other foreign matter, and you have an idea of crude petroleum as it is found in Nature.

It is interesting to note that practically the sole use of petroleum for some time after the first well was drilled was as a burning oil. The object of the refiner was therefore to produce as large as possible a percentage of paraffin from his crude. The lighter fractions were regarded as a necessary evil, and it became a very difficult problem to dispose of them satisfactorily. It was, of course, necessary to keep the flash point of the paraffin high enough to avoid the danger of explosion of the lamps in which it was used. Petroleum inspectors were employed to ensure that the paraffin on sale was not “adulterated” with the then valueless light petroleum spirit. No market other than as a source for lighting gas was found for this light spirit until the advent of the motor car.