Ron's Rambles

Horsepower. On a few occasions I have been asked questions such as “If my car has 70 horsepower does that really mean it has as much power as 70 horses?” To which the answer is simply “Yes” Back in the early days of steam engines It was apparent that engines were different in terms of the amount of work that they could do in a given time, in other words some were more ‘powerful’ than others and it was seen necessary to quantify this in some way. It was thought that they had an idea of how much work a horse could do in a given time and they could use that as a yardstick, but first they had to quantify how much that was. James Watt recognized that lifting a weight through a distance was work and the product of multiplying the weight by the distance lifted was a quantifiable measure of the work done. A good strong horse could pull a weighted cart up a hill faster than a lesser horse, although they would both have done the same amount of work. So time was another important factor i.e. the rate of working was determined by the power of the horse or the power of an engine. It is said that James Watt conducted an experiment using a horse to raise a weight up a deep shaft. I believe that he had the horse walking in a circle which implies a mechanism to convert that motion into one that could raise the weight. He concluded that his horse was able to work at a rate such that it could do 33,000 ftlb of work every minute and this was accepted as a unit of 1 horsepower. That has remained as the unit to this day. Of course, if James Watt had chosen a different horse he could well have obtained a different result, but that is no matter, all that was necessary was to establish a reasonable value. It was relatively easy to assess the horsepower of engines raising water from the mines since one could measure the amount of water lifted, the height raised and the time taken. With engines producing their power on a rotating shaft it was not so easy. A device for measuring power is called a dynamometer. For a rotating shaft a simple dynamometer was used in the form of a strap that was placed over the engine flywheel with a weight on one end and a spring balance fixed to the floor at the other. The weighted belt tended to act as a brake effectively trying to prevent the flywheel’s rotation. The difference between the weight and the reading on the spring balance gave the net force acting on the rim of the flywheel. Knowledge of the diameter of the flywheel and the rotational speed enabled them to determine the rate of working in ftlb/minute and hence the horsepower. As powers increased it was necessary to be able to apply greater braking force, this was done by using water dynamometers, effectively water pumps working against a resistance, the unit being free to swing about the same axis as the engine shaft and the force required to stop it rotating measured. More modern dynamometers are likely to use electrical generators. All dynamometers are, in effect, applying a brake on the engine – hence the term brake horsepower. In continental Europe they went through similar reasoning and different countries came up with their own units using metric quantities. The German horsepower unit is the pferdestartke which has the symbol ps or PS. It so happens that this unit of power is similar in size to the British horsepower, in fact 1ps = 0.986hp. You will often see engine power outputs of European cars quoted in ps units and there is a tendency to use a ps value as the horsepower. Of course these are all rather woolly units in this day and age when we have a scientifically consistent set of units with the joule as the unit of work and the watt as the unit of power. Engine power is measured in kilowatts, 1hp = 0.746kW. Unfortunately horsepower is so embedded in the minds of the motoring public that the unit is sure to live on for many a year yet.

The Oil Shop Following my thoughts on petrol retailing my mind wandered back to my childhood in the 1930s. Near where we lived in South London there was a small group of shops and one of the more important shops in the group was the Oil Shop. Everybody called it the oil shop but I do not know if that was a widely used name for that type of shop. Looking back now it was a very odd shop, it did sell oil, mostly paraffin, but there was also turpentine and these were sold from their tanks, you took your own bottle, often lemonade bottles, these had screw tops and a rubber seal. Digressing for a moment, those screw stoppers were made of some composite material but I never knew what that was. Some people would take a can, possibly an old petrol can. Petrol cans in those days had screw caps made of brass beautifully machined, they would also have brass spouts, such a contrast with the plastic cans of today The wooden floor boards around the tanks were totally impregnated with spillage. I am not sure if they sold white spirit but they did sell methylated spirits, it is a wonder that the place didn’t burn down. It was an odd shop because out the back they had large tubs of seeds, grain and cereals that were sold by the pound, whether or not people bought these to eat themselves I do not know but they were sold loose for pets and possibly horses. (Packets of breakfast cereals were widely available at that time.) These open tubs of grain did not seem to go well with the oil sales. Even more odd they sold mustard pickle, pickled onions, gherkins and beetroot as well as other pickles and, I believe, pease pudding. These products were sold loose and customers would take their own basins or jars. Then they sold many things that you might expect to find in an ironmongers’. You bought nails and screws by the pound, you would find plumbing items, hinges, handles, brackets and all the like. There was a limited range of paints, perhaps white, brown, green and cream, these were popular colour combinations for windows and doors in the thirties. They did sell a good range of small tins of Japlac, ideal for painting bikes I remember. I was a regular customer at the shop because it was my job to take my grandparents’ ‘accumulators’ to the shop to be recharged, another of the odd services provided by the oil shop. The batteries were used to power grandparents’ wireless set, a set employing thermionic valves, of course. These valves were heated electrically and consumed a lot of power compared to modern battery radios. Mains powered radios were available but at the time grandparents bought their ‘wireless’ we didn’t have any mains power. The shop also sold mantles for the gas lights and candles, but I was soon saved from having to buy those when mains electricity reached our house. We had two pin plugs, metal bulb holders, metal wall switches and no earth wire, rubber insulation that perished in time, it was enough to turn the hair of a health and safety inspector grey

Gramophones Thinking of old wireless sets reminded me that I recently came across an old Decca portable gramophone, a simple wind up machine, no batteries, no wires, no electronics and I was amazed at how good the sound quality was. I have heard old gramophones before and the rather tinny sound was typical, but this Decca was in a different class, playing dance music one could easily believe you were listening to a mono radio. I am surprised that it was possible to achieve that with such a simple device.