Early July 1997 our long-time correspondent from the Netherlands, Mr. Frits VAN DER VELDT, received a letter from J.K., an acquaintance of his who had contacted him several weeks earlier about an unusual object he had seen when in the city of IJmuiden. The letter was a reply to VAN DER VELDT's request to provide a written account of the sighting and a sketch of the object. We translate from Dutch:
On March 16, 1997, I was visiting some friends who live in IJmuiden (exact address omitted for reasons of privacy).
It was a dark, cloudy and rainy day.
At about four I left the house and got into the car to wait for my wife to come outside.
This took a few minutes.
I was in the car with the door still open.
I heard my wife talking to her girlfriend at the front door of the house.
Suddenly, my wife called out my name urging me to come out and take a look.
She sounded so excited that I thought something bad had happened.
I jumped out of the car and asked what was going on.
My wife pointed at the sky and said: "Take a look at that, there's something in the sky".
A couple of adults and a few children were also watching the apparition.
It was a UFO!
As I mentioned above, it was clouded that day. The wind was blowing quite hard actually, and came from the northwest.
The object was circular. As for the size, I don't want to make an estimate because it's almost impossible to do this from the ground about something that is in the air.
I already wrote that it was circular, but then again not quite. Something between oval and circle-shaped. The object consisted of a ring and a central space.
The ring had a darker colour than the central space and its size was about one third of the radius. The colour was grey, but of another kind of grey than the clouds.
The central space was of a lighter colour and transparent. Clouds that were of a darker colour than the light grey of the central space shone right through.
The object moved fast. Much faster than the clouds and in a straight line.
A roof of a house obscured the object from view. We were standing in the street, perplexed.
One thing was clear: we had seen a UFO.
- Letter from J.K. to Frits VAN DER VELDT dated July 1, 1997.
Perusing the newspapers for additional sightings of this highly unusual daylight object, we came across the following story, published in a local paper on Thursday, March 20, 1997 :
Lenticularis causes commotion on hockey field
It's Sunday afternoon, a quarter to four. Alongside the artificial grass field of KHC Strawberries a few hundred spectators are following the hockey top match between the First Male Team and Alliance from Heemstede, when all of a sudden something strange happens. From one moment to another nobody is interested anymore in corner penalties and yellow cards. Amazement, and especially disbelief rule. Fingers are pointed at the grey sky. From the west, the wind is pushing forward a round, flat and hollow cloud.
Sometimes it looks oval, but the phenomenon - a natural one of course - always regains a perfect round shape. At first sight it looks as if someone is smoking a cigar and blowing rings into the air. Only, in this case it has to be the Big Friendly Giant, the creature from the book by the same name written by Roald Dahl, because the cloud has a diameter of several tens of metres. Calmly, the mysterious cloud drags itself along from west to east. After a few minutes, when the cloud has disappeared behind the trees, things calm down again and the hockey game regains the attention of the crowd.
People who just arrive react to the story with the same amount of disbelief as those who have just seen it happen with their own eyes. There is laughter, until, a couple of minutes later, the same phenomenon - be it less distinct - appears above the Telstar stadium. The same scenes unfold, and again people are staring at the sky with their mouths open.
Then the clouds are no longer seen. It happened two times within ten minutes.
Explanations collected by the author of the above news article were twofold: "the searchlight of a party boat" (according to an - obviously ill informed - police spokesman) and a "lenticular cloud" (according to a meteorologist).
And yet, the comparison given by the sports journalist ("as if someone is smoking a cigar and blowing rings into the air") leaves little room for doubt: what is described here are plain and simple smoke rings. Many people (meteorologists included) are indeed unaware of the fact that metres-wide smoke rings cross our skies now and then. Probably J.K. saw one of these rings just prior to its arrival at the Telstar stadium (the stadium is only 1.2 km - 1,097 yards - southeast of the house where his friends live).
Not only the date (Sunday, March 16), also the time of the sighting ("at about four") matches that of the hockey match incident ("a quarter to four").
The wind had been blowing from the west-nortwest all day. Its speed was between 8 and 10 knots at ground level, and close to 25 knots at an altitude of about 200 m (656 feet). The cloud base was at 800 to 1,000 m (2,625 to 3,280 feet). At that altitude, the wind was blowing at speeds of between 27 and 29 knots .
The mention that the unidentified object moved "faster than the clouds" can be explained by the perspective effect by which objects that are close by appear to move faster than objects at greater distances moving with the same speed (much like when you see a toy balloon, a plastic bag or a piece of paper move rapidly under a cloud cover).
The origin of the ring was not too difficult to trace: there is an industrial zone bordering the North Sea, about 2.5 km further northwest of IJmuiden. Probably black smoke rings had escaped from one of the big chimneys at the steel factories which are located there.
The witness mentioned that the "central space" was transparent and of a lighter grey than the ring itself. This too is fully compatible with other descriptions and photos of smoke rings. The central part of a smoke ring often looks slightly darker than the sky because of the curling action of the smoke that pushes some of the smoke particles toward the centre of the ring. With the thicker smoke on the periphery of the ring forming a wall, the smoke inside the ring gets trapped in this way. A transparent blanket of smoke is then created and disperses only when the ring itself dissolves. In some instances white/grey cumulus like cloudlets have been reported to form in the open space inside black smoke rings. One such cloud was photographed in 1957 near Fort Belvoir, Vancouver, USA. Another spectacular photo of this cloud-in-ring phenomenon was taken in 1974 in Viborg, Denmark.
Additional information and images of metres-wide smoke and steam rings can be found in our picture galleries under ring-shaped vortices.
A rare but nonetheless typical sighting of a smoke ring drifting away from a nearby industrial complex.
 "Lenticularis zorgt voor commotie op hockeyveld" in De Hofgeest of March 20, 1997.
 Data gleaned from balloon soundings carried out at De Bilt, the Netherlands, at 1:00 pm and 7:00 pm.
Full data can be consulted at weather.uwyo.edu.