100 YEARS AGO

An interesting and detailed account of Count von Zeppelin's successful trial trip of his navigable balloon on July 2 is given in Die Umschau by an anonymous author, who has endeavoured to dispel the somewhat exaggerated reports which have been circulated as to the success or failure of the experiment. It is pointed out that the delay in the ascent, which some persons attributed to an accident, was really caused by the wind being too strong at the time originally proposed for the trip. The wind-velocity at the time of starting was 5.5 metres per second, and the balloon was actually driven forwards for a short time in the face of this wind... The wind causing the balloon to drift towards the shore, a descent was made in order that Count Zeppelin might land on the water (to use an Irishism), and thus have his machine towed back by steamer. The descent was very gradual, the cars gently sinking down to the water without the sudden jerk which is commonly experienced in an ordinary balloon.

From Nature 23 August 1900.

50 YEARS AGO

If we slide one solid body over another, there is a resistance to the motion which we call friction. What is the cause of this, and what is really happening at the interface between the solids during sliding? It is usually considered that friction is a nuisance, and from the earliest times man has made ingenious attempts to eliminate or to diminish it to as small a value as possible. It is not so much the work we have to do in overcoming the friction—the power loss—which is important, although this can be considerable. In a modern motor-car, for example, about 20 per cent of the power is wasted in overcoming friction… The real trouble is the damage that is done by the friction—the wear or seizure of some vital part of the machine. It is this factor, perhaps more than any other, which limits the design and which shortens the effective life of, say, an aero-engine or other complex machine. Nevertheless, the credit side is considerable: if the coefficient of friction were much less than it is, walking would be impossible and we should have to use cog wheels or perhaps some system of suction pads like an octopus to get about at all. Conversely, if it were much higher than it is, we should just stick fast wherever we were put.

From Nature 26 August 1950.