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| Forces on a falling insect. © Eugene Brennan |
Wednesday, June 10, 2026
How Can Insects Survive Falling From a Height?
Sunday, June 07, 2026
Learn How to Solder: A Complete Guide for Beginners
Saturday, June 06, 2026
Kippure TV Mast Visible From Kilcullen
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| Kippure in the Wicklow Mountains, photographed from Kilcullen. © Eugene Brennan |
Thursday, June 04, 2026
Why Is Most of an Iceberg Under Water? And How Much?
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| Original uncaptioned image Lurens, public domain image via Pixabay.com |
Ninety Percent of an Iceberg Is Below the Waterline
Icebergs can be massive, but did you know that you're only seeing literally the tip of them above the water? Yes, up to 90% of an iceberg's volume can be under water. But why does that amount sink and not just float above sea level like the rest of it? In this article we explore why.
What's the Difference Between Analogue and Digital?
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| © Eugene Brennan |
Analogue vs. Digital
We often hear about analogue and digital in the context of communications, sound recording, cameras, TV, radio, and electronic devices. But what exactly is the difference, and is digital better than analogue? Why has digital replaced analogue in audio, digital imaging, and electronic communication?
Vodafone Internet Service Down After Thunderstorm
Tuesday, June 02, 2026
Why Is Binary Used in Electronics and Computers?
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Why is binary used in electronics? Geralt via Pixabay.com |
Why Do Computers Use Binary?
The binary numbering system is the basis for the storage, transfer and manipulation of data in computer systems and digital electronic devices. This system uses base 2 rather than base 10, which is what we are familiar with for counting in everyday life.
How to Convert Decimal to Binary and Binary to Decimal
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| Binary number and its decimal equivalent. © Eugene Brennan |
Base 2, the Basis for Binary Code
The base 2, or binary numbering system is the basis for all binary code and data storage in computing systems and electronic devices. This guide shows you how to convert from binary to decimal and decimal to binary.
Sunday, May 31, 2026
How to Convert Hex to Binary and Binary to Hexadecimal
Saturday, May 30, 2026
The Andromeda Galaxy: "It's Big, And Also Faaarrr Away"
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| The apparent size of the Andromeda Galaxy, compared to that of the Moon. AI image created by Grok. |
Saturday, May 23, 2026
Loading Data for the Kilcullen 38 kV Substation.
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| Loading data for the Kilcullen 38 kV Substation, courtesy ESB Networks. |
The table shows summer and winter loads in megawatt (MW) for transformers T41, T42 and T424.
Sunday, May 17, 2026
It Came From Outer Space....
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| Nostoc commune (Latin name), also known as "jelly fungus". © Eugene Brennan |
Well not quite. This is probably Nostoc commune (Latin name), also known as "jelly fungus", "star jelly" or "witch's butter". It's not actually a fungus, but a colony of bacteria. There's loads of it in a patch on my yard, but it sometimes grows on lawns. It's extremely slippery on a lawn. Apparently it's eaten as a salad in the Philippines when dried out. I'm a fussy eater so I won't be trying it anytime soon.
More information on jelly fungus here on Wikipedia.
Friday, May 08, 2026
Off-Road Lanes for Cycling in Kildare and Wicklow
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| Lane from Barretstown to Bishopshill Commons. © Eugene Brennan |
Tuesday, April 28, 2026
Available Substation Capacity in Ireland
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| Information on substations. Image courtesy ESB Networks. |
This interesting interactive map on the ESB Networks website shows transformer capacities. A "substation" indicated on the map could be an actual town substation like the one at Sunnyhill, with 1, 2 or more transformers and associated switchgear and circuit breakers, or a transformer in a cabinet or small building (common in the newer housing estates).
Sunday, April 26, 2026
What Is the Ground Wire For?
Saturday, April 25, 2026
Re-Discovering the Mill Stream Arch
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| One mill is marked on the OSI c.1837 first-edition six-inch map. Image courtesy the National Library of Scotland, licence CC-BY. |
I hadn't seen it since around 1982 or '83. I thought it was covered with scrub and brambles over the decades, but not so. This is a good time of the year to investigate it before the brambles get going. My theory is that it could have been the opening to a culvert/mill race that diverted water to a second mill in the adjoining field beside the cemetery car park or it may have been the return feed to the stream. One mill is marked on the 6-inch, first-edition OSI map and was located just over the wall from where the bins used to be kept in the cemetery. The ruin is still there. There's an arched culvert under the Mile Mill road, south of the lodge, that fed water to this mill.
I think the arched opening into the stream is unlikely to be a latrine outlet or drain as it's too wide. I thought most of the arch was submerged below the waterline, but possibly the bed of the stream has dropped over the last four decades due to erosion. Anyway, I didn't have a camera with me. That's a shame because the arch was nicely lit up by the setting sun.
Will investigate further tomorrow and take some photos.
The map above is a ChatGPT-sharpened version of a screenshot of the c. 1837 first-edition six-inch map available on the National Library of Scotland website. The scans appear to be a bit clearer than those available on Tailte Éireann's Irish Townland and Historical Map viewer.
Map reproduction licence CC-BY, courtesy the National Library of Scotland.
Thursday, April 23, 2026
YouTube Requirements and Broadband Speed
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| Connection speed required for YouTube. Image from Google Help |
Unless you have lots of people in your home feeding off your Internet service and sharing the bandwidth, ultra-high-speed connection promotions such as "Gigabit broadband" are just marketing hype. The table above shows the recommended connection speeds from Google for streaming video from YouTube. Vodafone keeps trying to sell me such a service using a fibre-optic connection that replaces copper wires to the cabinet and which would increase my speed from 100 Mbps to 1 Gbps, but I'm stubbornly refusing as the current speed is perfectly adequate. A faster connection probably increases upload speed (which I think is normally about one tenth of download speed), but most people aren't in a hurry when uploading, unless they can't wait to backup thousands of photos or put their latest video online. Eventually I'll have to give in, because copper lines, which Vodafone rent from Eir, will ultimately be replaced. The process is slow, because there are legacy systems that still require them.
I ring Vodafone every year, three months before my contract is due for renewal and negotiate a loyalty discount, getting a six-month discount. It's only €5 per month for 6 months, but better than nothing.
A Child Can Push Harder Than a Lawn Mower Blade
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| AI image generated by Google Gemini. |
Did you know that a child can probably produce more torque using their arm, than a lawn mower engine can generate to turn the blade? Surprisingly, the figure for the torque of a 5 hp engine used on a mower is 7 to 10 foot-pounds (ft·lbf) in the imperial system or 11.5 to 13.6 newton-meters (Nm). Applied torque is simply force multiplied by distance, so 1 pound-force applied over a distance of 1 foot from a pivot is 1 foot-pound. In the metric system, the unit of torque is the newton-metre (Nm). A torque of 1 Nm is equivalent to one newton—the SI unit of force—applied over a distance of one metre. The speed of a lawn mower blade is more important than torque, and blades are driven directly by the crankshaft without reduction or overdrive gearing. Blades typically spin at the engine speed of around 3000 RPM, giving a blade tip speed of around 200 mph, or 90 metres per second.
As we saw in the article Interesting Facts - What is Torque?
power = torque x angular rotation speed
So while a child may be able to exert more torque with their arm than a mower engine can exert on a blade, they wouldn't be able to match its power. Another piece of the jigsaw is that the quoted figure of 11 to 13 Nm is for the drive torque from the engine. Since a blade is spinning at around 3000 RPM, it has a lot of inertia. The technical term for this when a rotating body such as a flywheel or blade is involved is moment of inertia. When a blade slows down as it impacts grass, the change in angular momentum creates a force, just like the way a car or any linearly-moving object creates a force as it slows down due to friction, or when it hits something (think of the huge force produced by a hammer, typically many tonnes, when it hits a nail). So the force produced by a blade as it impacts and shears grass is much greater than the force that the engine itself could have generated.
Note: You may be wondering why "newton" in "newton-metres" above isn't capitalised. The unit is named after the English scientist Isaac Newton. It's not a typo. In the International System of Units (SI), or Système international d'unités, units named after a person are not capitalised. However, the symbol is, N in this case, Units are normally lower case, as are prefixes. However, prefixes over one million are capitalised—so kilometres is km, but gigahertz is GHz.
Thursday, April 16, 2026
Cantilevered Boardwalks For Motorway Bridges?
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| Bridge over M9 Kilcullen Bypass on Sunnyhill Road. Image courtesy Google. |
When
Kildare County Council, or whoever was responsible, produced the spec
for this bridge, (and the one over the M7 at the Bundle of Sticks
Roundabout outside Naas), they left out foothpaths. Maybe it was lack of
common sense and an attitude of "Sure, only cars go out there". Or
perhaps it was due to penny pinching and lack of foresight and a narrow
bridge was cheaper than one a couple of metres wider? Anyway, I'm
wondering could boardwalks/cantilevered foothpaths be fixed onto the
sides, exterior to the parapets?
It would obviously
be impractical to install foothpaths on the inside of the parapets due
to to both lanes being reduced in width. As it is, cars can't pass
pedestrians safely without partially moving into the other lane. An article by Paul MacDonald, Kildare National Roads Office, on the construction of the M7 Newbridge Bypass and M9 Kilcullen Bypass is
available on the Kilcullen Diary here.
The section about the earthing of the steelwork of the underbridge for the River Liffey is interesting—High voltage pylons can induce voltages and currents in conductors, potentially leading to different and hazardous potentials between isolated elements of a structure. Bonding them together eliminates these voltages and earthing a structure pulls the voltage down to ground (similar to the equipotential bonding in bathrooms, where metal objects such as drains, radiators, towel rails, water pipes and metal baths are bonded together):
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| Bridge over M9 Kilcullen Bypass on Sunnyhill Road. Image coiurtesy Google. |
Wednesday, April 15, 2026
How to Calculate Bolt Circle Diameter (BCD) for Chainrings and Bash Guards
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| Bolt circle diameter (BCD). © Eugene Brennan |
What Is a Bolt Circle Diameter (BCD) or Pitch Circle Diameter (PCD)?
As you may be aware, if you've found this guide, a bolt circle is an imaginary circle that passes through the centre of the bolt or screw holes in a round pattern. This is typically a wheel hub on a vehicle, chainring on a bicycle or flange on a pipe. The diameter of this circle is known as the bolt circle diameter (BCD) or pitch circle diameter (PCD).
Typically, BCD is quoted for chainrings on bikes and the bash guards that cover them, and you can calculate it by measuring the distance between the mounting holes of the chainring on the spider. If you need to order a part for a bicycle or check the BCD of a flange and can only measure the bolt hole spacing, you need to know the formula for working it out. Alternatively you can skip to the end of this guide where there are tables for various bolt spacings.





















