Scientific Equipment on HMS Challenger

Hello! This is Peter (the Challenger Project’s volunteer) writing. I’m a history student at the University of Exeter, and I’ll be working here until the end of June.

This map was made using data from the Challenger expedition

This map was made using data from the Challenger expedition

As you probably know, the Challenger project is bringing together data from museums all over the country. It’s great that there’s so much information, but it can be pretty overwhelming! HMS Challenger stopped at over 400 locations (at 354 unique stations) during its trip around the world. At each of these stations, the crew and scientists took detailed scientific readings about the sea and the weather with barometers, hydrometers, thermometers and other instruments, as well as dredging or trawling the seabed for specimens. Just the data we have amounts to well over 15,000 specimens! So far, most of what I’ve been doing is going through spreadsheets of information, matching up station numbers with data like ocean depth and temperature, or filling out taxonomic data for several hundred specimens (so far!).

This temperature data was collected by the scientists on board the Challenger.

This temperature data was collected by the scientists on board the Challenger.

Something more interesting I’ve been looking at recently, though, is the equipment used on board HMS Challenger. Though the Challenger was a corvette, a small war ship, most of her guns were removed to make way for all the scientists, their equipment, and a pair of laboratories. A small steam engine was also fitted to the upper deck, to be used as a sort of winch for towing, raising and lowering the dredge and trawl. The dredge was a net fitted to an iron frame which would be dragged along the seabed on a long rope, stirring up the bottom and scooping up samples. The trawl was a more simple net which could be used where the bottom was smoother.

The dredge could also be dragged behind the Challenger's steam pinnace.

The dredge could also be dragged behind the Challenger’s steam pinnace.

The specimens brought up would be sorted in the port-side natural history laboratory, which was equipped with microscopes and a wide variety of bottles, jars and spirits in which to preserve animals and invertebrates. Botanical specimens would be pressed and dried out in a warm area near the ship’s funnel (this was found to be far more efficient than using the purpose-built press that they brought with them!), and then everything would be catalogued and put into storage in the hold.

In the Natural History Laboratory, specimens could be examined and preserved with the use of scientific equipment. Note the microscope.

In the Natural History Laboratory, specimens could be examined and preserved with the use of scientific equipment. Note the microscope.

But it wasn’t just the living creatures that they were interested in. At one point, barometer and air temperature readings were taken every two hours for a whole year! At every station, the sea temperature was taken at various depths with a special pressure-resistant thermometer, and samples of the sea floor (using a Baillie’s sounder) and sea water at various depths (using a slip water bottle or a stopcock water bottle) were brought up for analysis. This was done in the starboard-side chemical laboratory. This was equipped with state-of-the art equipment for testing what gases were dissolved in the seawater, a glass-blowing bench and a hanging spirit lamp, designed to heat substances without spilling them in rougher seas.

This sounder was used to measure the depth of the ocean and collect samples from the seabed.

This sounder was used to measure the depth of the ocean and collect samples from the seabed.

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Measurements and equipment on HMS Challenger

As I explained in our first post, the HMS Challenger expedition aimed to find out the chemistry and physics of the deep-sea. However, what and how did they measure?

Measurements and equipment used on HMS Challenger

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To measure temperature: Miller-Cassela thermometers

One of the main components they wanted to measure was surface, bottom and intermediate temperatures of the sea. For almost all the observations, the Miller-Cassela thermometer was used. This was a  minimum and maximum thermometer (in other words, it  showed the minimum and maximum temperature of the water). As a series of temperatures were measured at different depths, this type of thermometer could be relied upon..to a certain extent. More accurate thermometers were needed at deep depths but the plan to get any was unsuccessful before the end of the expedition.

To measure specific gravity: Piezometers and hydrometers

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First off – what is specific gravity? In simple terms and in this case, it is the comparison of the density of sea water with the density of pure water. This all gets a little confusing but I will try to explain it simply.

Specific gravity was measured using devices called hydrometers and piezometers, measuring mass and water pressure. This can then be used to calculate density and so specific gravity.

So why was this useful for the expedition?  Firstly, water pressure was used to measure depth and you could see how the density of the seawater changes at different depths. It was also used to make sure that the temperature was recorded accurately – the thermometers gave you the minimum and maximum temperature and this would be accurate if at all areas the deeper the water the colder it gets. However, this is not always the case. For example, ice is less dense than seawater and so floats on top, despite being colder than the water below it. The crew worked out that a fall of one degree of temperature had the same effect as an increase of pressure equal to 430 fathoms. From this, temperature could be recorded correctly. How to measure and what to measure with was certainly well thought out! Now on to how they collected water – a little easier on the brain!

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To collect water during the HMS Challenger expedition: Buckets and Bottles

When collecting water, water from the surface was collected simply with a bucket. Water from the bottom, however, was collected by specifically designed instruments, for example the Slip Water-Bottle. This was basically a brass cylinder that takes in water once it reaches the bottom. A similar water bottle, called the Stop-Cock Water Bottle, was used to collect water at intermediate depths.

 
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So that is just some of the main equipment used aboard HMS Challenger to gather important data. The temperatures recorded are still being used now to compare how the ocean’s temperature has changed over time so it was well worth the effort.

That is me for now…in the next blog post I will show you examples of some of the data collected from a station, including some specimens that were found. Speak soon!