| On Location III |
| In summer I sometimes go cycling along a dirt road (or "sand path", as we - much more fetchingly - call it in Dutch). Surprisingly, this path is located only minutes away from the inner city. A long road it's not (although in all fairness it does wind a little). A row of concrete piles on either side make the path inaccessible to any vehicle that has more than two wheels, including wheelchairs. Nobody demurs: this is, after all, a dirt road. A typical example of what we refer to as "overruled" in Dutch, as we will see. |
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It's starting to rain, forthright drops starting to come down. A butterfly
continues flying about unperturbed. It has taken me years to figure out why
animals respond more quickly than human beings, not taking into account
their differences in size and physiology: in animals, the distance which the
electrical pulses have to travel to reach the central control room is simply
shorter (it's a funny thought that rather than actually seeing things, all
we do is decode pulses provided our consciousness allows). I envy the
animals in this respect Which nevertheless prompts the question as to how a butterfly manages to remain airborne while it's raining. Am I correct in assuming that a drop of water probably outweighs a butterfly and if the latter were to be hit by the former, in addition to receiving quite a blow it would end up soaking wet and thus, not in a terribly fit flying state? And yet this is something which butterflies are evidently quite happy to deal with. I already knew that the flying pattern of the butterfly is inspired by safety considerations rather than clumsiness, as I once thought (and perhaps I wasn't the only one). This prompted the question as to whether I would be able to calculate the butterfly's response time on the basis of its ability to avoid falling rain drops (provided it wasn't raining too hard). My mental abacus started clicking. First element: number of drops falling per arm's length, per second, at an average width of 8 centimetres, to obtain the number of drops per square metre. Second element: the rate at which a drop of water falls. It is an established fact that the human eye is capable of seeing a drop of water fall. Provided the drop makes a sufficiently long drop (pardon the pun), we can even catch it. It is also an established fact that the human hand is incapable of catching a butterfly. These two facts imply that butterflies more than outclass human beings in the speed department. If we assume that a butterfly is twice as fast as a human being, this would mean that the butterfly is capable of catching droplets at half the distance compared with us. Of course the butterfly will use this skill to duck and dive rather than catch the drops full-on, but that's not germane to the issue. I had a feeling that further substantiation would be in order if the issue were to be resolved in a truly satisfactorily manner, and so I went back to the actual rain drops making up the distinctly mellow shower during which I was having all these thoughts. I counted less than one rain drop per second. It would suffice to observe the rain for a mere minute, and so there was really no need for me to calculate the square metre value: you don't need to be a rocket scientist to appreciate that this wouldn't even begin to strain the capabilities of our butterfly. On the one hand, it is only with great difficulty that the human arm, moving along in a straight line, will succeed in avoiding just the one drop of rain, let alone that it will achieve this while making erratic movements in a multi-droplet scenario. On the other hand, the human hand is incapable of catching a butterfly in flight. For this it needs a net on a stick. All of which can only mean that the butterfly goes much faster - faster, in any event, than the size of the water drop multiplied by the specific density and divided by the drag coefficient times the distance of the drop. At least twice as fast, in fact. Looking at this entire body of proof, my conclusion is that a butterfly simply sees the rain drops coming and flies around them. |