IMPORTANT
NOTE: THIS MATERIAL IS COPYRIGHTED BY THE AUTHOR AND MAY NOT BE REPOSTED,
REPRINTED OR OTHERWISE USED IN ANY MANNER WITHOUT THE WRITTEN PERMISSION
OF THE AUTHOR
SCIENCE IN CRIME DETECTION - 23
KNOWING ABOUT CAR HEADLIGHTS
-Dr. Anil Aggrawal
I had a tremendous response for my article " Defence Wounds", published in the January,1995 issue of Crime & Detective. I have had some interesting letters in this respect. Mrs. Anita Gupta, an NRI has written to me from Perth, Australia ( Don't ask me how the magazine reached her! She hasn't indicated it in her letter. Judging by the quality this magazine is gradually gaining, I presume, some relative sent it to her to let her know the quality stuff, we are producing on crime, right here in our own country). For those of you who have missed out this article, I may recapitulate that on page 39, I had mentioned that in cases of attempted rape, the defence wounds may be on the legs of the victim. She wants to know that if we can do that, why is it so much difficult to catch the rapists? Why can't we say just from seeing the defence wounds that the woman has been raped? Apparently Mrs. Anita is much perturbed over the age-old question of rape. It is understandable too as she is herself a woman, and has every right to know about the welfare of women.
Well Anita, the situation is like this. In cases of rape, you might get defence wounds on the legs, but it is not a must. In other words, you may or may not see defence wounds in a case of rape. Only when you see the defence wounds, can you say with certainty that the woman had tried her level best to resist the advances of the rapist. But if she was, say, too terrified by the appearance of the rapist himself, she would be too scared to even move, and in such cases it is doubtful, if she would sustain any defence wounds on her legs at all.
This time I am going to tell you about a very interesting situation in which forensic science can be used. In fact I was involved in one such case when I was attached at the department of Forensic Medicine in Dundee, Scotland.
On 6 June 1990, at about 11 pm, there was a massive accident on the Dundee highway. A fast moving car hit a pedestrian, crossing the road. The onlookers gave the evidence that the headlights of the car were not on, and that's why the unfortunate victim ( a person by the name of Scott) could not see the car. When the car was examined, it was found to be badly damaged too, as it had hit the lamp post on the kerb after hitting Scott. Both the headlights were broken, the radiator was crushed, and the front window pane totally shattered. When the driver of the car was questioned regarding his headlights, he asserted that he had indeed put on his headlights, and Scott must have died of his own carelessness. The onlookers insisted that the headlights were not on, but the driver (a person by the name Bailey), did not agree. The headlights were badly damaged and Bailey knew very well that no one could now prove whether the headlights were indeed on or not. When the police brought the problem to me, I said that I could perhaps solve their problem.
"You mean you could say, whether Bailey had put on the headlights at the time of the accident?" asked the police constable Fernando in total surprize, "You must be joking. The car lights have completely smashed. There is no way you could say whether Bailey had put on the lights at the time of accident or not."
"Are the lights broken?" I asked Bailey
"Absolutely", he replied.
"Don't worry Fernando. You will have your man by tomorrow. Just show me where the car is. I want to take away the bulbs to my laboratory." I said.
And the next day, I told him that Bailey was moving with his headlights off. The court admitted my scientific evidence and Bailey got 2 years rigorous imprisonment in jail. Were it not for my scientific evidence, Bailey might have been a free man today.
You must be wondering as to how I could produce this magic. Well, to understand it fully, we will have to take a closer look at the structure of the car headlights, or of a common household bulb.
We are all familiar with the common household bulb. Take one out and look at it carefully. There is a thin wire which goes through it. This wire is made up of a tough metal Tungsten. Tungsten has a very high melting point. This means that one would have to heat the tungsten to massive temperatures before it would turn into liquid. A temperature of about 3650o C is required to melt tungsten. It may be sufficient to tell here that water boils at about 100o C, and most other metals including iron would melt at much lower temperatures than that at which tungsten melts. This unique property of tungsten makes it very suitable for use in light bulbs. If, say, iron were used as a filament in bulbs, it would melt very soon and the bulb would fuse in no time.
When a current is passed through the tungsten (by switching on the current), the tungsten gets heated to a very high temperature. At high temperatures, it begins to glow and gives light. Of course, all this happens in a flash of second, and you don't even know what has happened. The manufacturers take away the air from the bulb, producing a vacuum inside it. The air has oxygen in it, and if air were there inside the bulb, it would burn away the tungsten. Nothing can get burnt in the absence of air, however much you may heat it. Scientifically speaking we say tungsten would get oxidised in the presence of air or oxygen. Oxidised or burnt tungsten is useless for producing light. Because of this reason, the air has to be evacuated from the bulb.
When tungsten is heated within the bulb, it starts glowing and gives off the light. When the current is switched off, the tungsten returns to its original temperature and it stops glowing. The cycle keeps repeating like this indefinitely. But during an accident, when the bulb breaks, the air gushes in suddenly. If the light would be on at this time, the tungsten would be red hot. Since it would be red hot, it would immediately get burnt when oxygen rushes in (or in scientific words "it would get oxidised". We would be using the scientific terminology only henceforth.) The noticeable and most important thing is that if at the time of breaking of the bulb, the tungsten filament was not red hot, the question of it getting oxidised just does not arise. So the whole problem boils down to this. Was the tungsten filament found in the broken car headlight oxidised or not. If it is found in an oxidised state, the car headlight must surely be on at the time of the accident. But if the tungsten is in its normal state, the headlight must be off.
How to find out whether the tungsten was oxidised or not. This is a very simple problem for scientists. Fortunately even a layman can understand this. When tungsten begins to get oxidised (or burnt), it begins to change its colour. It is first of all normal cream white (which is its normal colour). Then as the burning process continues, it changes its colour like a chameleon as follows:-
Straw-yellow -> Green -> Green-blue -> Intense-blue -> Violet -> Purple-brown -> Chocolate -> Grey-black -> Charcoal -> Yellowish white.
Let me explain the above sequence of colours in a little more detail to you. If you burn two filaments of tungsten for different periods of time, say for one and two hours respectively, then the one which was burnt for two hours would get burnt more thoroughly, and would assume a colour much down the line in the above series. Take another example: Suppose somebody gives me two burnt filaments of tungsten. One of them is of a green colour and the other is chocolate colour. Now by knowing the above sequence of colours, I can easily say that the one with the chocolate colour burnt for a longer period and acquired a higher temperature. Because when tungsten is burnt, it always acquires chocolate colour after it had become green - never the other way round.
Look at the following figures. These show you how tungsten looks at various temperatures. Fig 1 shows five separate tungsten filaments removed from car head lamps and heated in a furnace in the presence of air for different periods. The one on the extreme left is pure unheated tungsten. After that are various filaments which have been heated for increasing periods of time. You can judge from their colours how hot they should have been at the time of photographs.
Fig 2 shows an experimental bulb break when the bulb was on. See the colour of the tungsten. It has completely changed. You can now say why this happened. The air rushed in at the time of bulb break and oxidised the tungsten filament, and thus changed its normal cream-white colour.
Fig 3 shows a similar experiment, when the bulb was on for a longer period of time. Here also you can see various colour changes. Of course when you see the actual tungsten filaments you appreciate the colours much better. It takes a little bit of training too, before you begin to feel convenient with these colours.
Coming back to our original case. When I examined the tungsten filament of Bailey's headlights, I found that the filament was in its normal cream-white colour. It could mean only one thing - that the tungsten filament was cool at the time of impact. Why was it cool? Obviously because the headlights were off!
***
IMPORTANT
NOTE: THIS MATERIAL IS COPYRIGHTED BY THE AUTHOR AND MAY NOT BE REPOSTED,
REPRINTED OR OTHERWISE USED IN ANY MANNER WITHOUT THE WRITTEN PERMISSION
OF THE AUTHOR
